I tested the above kernel on a ThinkPad X1 Carbon 7th with a Thunderbolt Dock 2nd Gen.


Below it the result when inserting cable into local Ethernet:

u@u-ThinkPad-X1-Carbon-7th:~$ ip a 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 98:fa:9b:1d:f8:01 brd ff:ff:ff:ff:ff:ff
    inet 10.8.8.38/24 brd 10.8.8.255 scope global dynamic noprefixroute enp0s31f6
       valid_lft 375sec preferred_lft 375sec
    inet6 fe80::5af7:b91b:8317:9006/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever
3: wlp0s20f3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 38:00:25:62:c5:1e brd ff:ff:ff:ff:ff:ff



Below it the result when inserting cable into Dock Ethernet:

u@u-ThinkPad-X1-Carbon-7th:~$ ip a 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 98:fa:9b:1d:f8:01 brd ff:ff:ff:ff:ff:ff
3: wlp0s20f3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 38:00:25:62:c5:1e brd ff:ff:ff:ff:ff:ff
4: enxe04f439597fa: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether e0:4f:43:95:97:fa brd ff:ff:ff:ff:ff:ff
    inet 10.8.8.25/24 brd 10.8.8.255 scope global dynamic noprefixroute enxe04f439597fa
       valid_lft 582sec preferred_lft 582sec
    inet6 fe80::26ef:5ee3:a28b:3622/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever


Below it the result when inserting cable into Dock Ethernet and enabled Mac Pass Through in BIOS:

u@u-ThinkPad-X1-Carbon-7th:~$ ip a 
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 98:fa:9b:1d:f8:01 brd ff:ff:ff:ff:ff:ff
3: wlp0s20f3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether 38:00:25:62:c5:1e brd ff:ff:ff:ff:ff:ff
4: enxe04f439597fa: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether e0:4f:43:95:97:fa brd ff:ff:ff:ff:ff:ff
    inet 10.8.8.25/24 brd 10.8.8.255 scope global dynamic noprefixroute enxe04f439597fa
       valid_lft 184sec preferred_lft 184sec
    inet6 fe80::26ef:5ee3:a28b:3622/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever




so, in the 3rd testing, the IP still get from Dock's address e0:4f:43:95:97:fa, it seems the Mac Pass through did not work.