It is done in U-Boot. If you add a line ethaddr=what-ever-mac-you-want to uEnv.txt it will be added automatically. See https://github.com/longsleep/u-boot-pine...1p1.h#L373 - if you do not see this behavior your image U-Boot is too old.
Forgot to say that the images also automatically add that line to uEnv.txt on boot if it is not there.
Forgot to say that the images also automatically add that line to uEnv.txt on boot if it is not there.