This device shares the network config with v4, thus the WAN MAC
also needs to be fixed the same way. However, the partition
where the MAC address resides has been changed.
Based on: https://github.com/openwrt/openwrt/pull/1726
Tested-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>