The current MAC address assignment for the ASUS RT-AC51U is "wrong",
it actually should be the same as for the RT-AC54U. Fix it.
MAC assignment based on vendor firmware:
2g 0x4 label
5g 0x8004 label +4
lan 0x22 label +4
wan 0x28 label
Thanks to Davide Fioravanti for checking this on his device.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>