Facing the same issue with X540-AT2.

When I PXE boot a VM it PXE boots just fine. On that same MAAS installation (tried 2.1.3 and 2.2b2) physical NIC, on the same machine where VM booted just fine, fails to PXE boot.

tcpdump shows enormous ARP traffic:

08:31:14.649459 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649482 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649493 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649504 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649516 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649528 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649551 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649562 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649573 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649597 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649607 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649619 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649642 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649653 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649664 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649675 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649687 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649709 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649720 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649732 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649744 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649767 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649778 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649789 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649801 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649813 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649835 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649846 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649858 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649869 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649880 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649904 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649906 2c:60:0c:cd:0f:cf > 2c:60:0c:f9:41:f0, ethertype ARP (0x0806), length 42: Reply 172.16.7.2 is-at 2c:60:0c:cd:0f:cf, length 28
08:31:14.649929 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649932 2c:60:0c:cd:0f:cf > 2c:60:0c:f9:41:f0, ethertype ARP (0x0806), length 42: Reply 172.16.7.2 is-at 2c:60:0c:cd:0f:cf, length 28
08:31:14.649953 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649976 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.649978 2c:60:0c:cd:0f:cf > 2c:60:0c:f9:41:f0, ethertype ARP (0x0806), length 42: Reply 172.16.7.2 is-at 2c:60:0c:cd:0f:cf, length 28
08:31:14.649998 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46
08:31:14.650000 2c:60:0c:cd:0f:cf > 2c:60:0c:f9:41:f0, ethertype ARP (0x0806), length 42: Reply 172.16.7.2 is-at 2c:60:0c:cd:0f:cf, length 28
08:31:14.650021 2c:60:0c:f9:41:f0 > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has 172.16.7.2 tell 172.16.7.101, length 46

This leads me to believe that the NIC is the culprit here, rather than MAAS.