Hi Daniel,
When using OpenWrt, we are dealing with this differently: The random address generated by Linux is made persistent on first boot for both ethernet devices:
https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/mediate...
And eventhough U-Boot at this point knows nothing about there being more than one Ethernet MAC it still sets the address stored in eth1addr for the Ethernet MAC pointed to by the 'ethernet1' alias.
However, to let U-Boot do that for you, we would need to change the Ethernet driver in U-Boot to expose all MACs rather than just one of them.
That is an interesting workaround, I will try it out.
In the meantime I managed to configure systemd-networkd to assign a permanent MAC address.
It is unfortunate that these boards don't come with preallocated MAC addresses which would remove the need for random ones.
Thanks, Leith Bade