LAN working on Minix NEO X7.
For now I gave up on trying to find the IO-pin that controls the LAN power on the Minix NEO X7 board.
By making a hardware modification, involving removing a voltage controller (because unfortunately 1 pin broke during the modification) and placing a wire to get the LAN power supply from another voltage controller, I got LAN up and running. I will leave it running for a couple of days to see if nothing breaks.
I can state that the drivers for the Realtek 8152B USB ethernet adapter are working.
