Hey Balbes150,
First of all, thanks for all the hard work getting mainline up and running on the Odroid N2! I'm using your latest unified gl12 non-desktop image, and it works wonderfully, with a few odd quirks.
Networking is a bit... Weird. I had to wipe the NetworkManager configs 4 times just to get the same config to stick between reboots. Setting the MAC address from the startup arguments did not work (as described in the original post), and NetworkManager only accepted it properly once I did the change from Cockpit (which is a great web server management tool, I can only recommend it). However the network config, even this way, is often dropped after a reboot, even though the config file exists in /etc/NetworkManager/system-connections...
Rebooting takes ages - up to 10 minutes, for some reason, and sometimes requires a full-on power cycle (pulling the PSU for 5 minutes from the board).