A difference I see between my two RPi3 is that workin one has ID_NET_DRIVER=smsc95xx, while the non-working one has ID_NET_DRIVER=lan78xx. In the latter, I can see that there is actually a valid ethernet address available in the device tree:
$ od -t x1 /sys/firmware/devicetree/base/soc/usb@7e980000/usb1@1/usbether@1/local-mac-address 0000000 b8 27 eb 90 3c c0 0000006
and it can be checked that such address belong to the RPi foundation.
A difference I see between my two RPi3 is that workin one has ID_NET_ DRIVER= smsc95xx, while the non-working one has ID_NET_ DRIVER= lan78xx. In the latter, I can see that there is actually a valid ethernet address available in the device tree:
$ od -t x1 /sys/firmware/ devicetree/ base/soc/ usb@7e980000/ usb1@1/ usbether@ 1/local- mac-address
0000000 b8 27 eb 90 3c c0
0000006
and it can be checked that such address belong to the RPi foundation.