The TP-Link firmware uses (primary_mac-1) as MAC-address
for the 5GHz WiFi. This applies the same behaviour to LEDE.
Currently, the MAC-address is retrieved from eth1, which
does not exist on the Archer C7 v4. As a result from this,
every C7 v4 with LEDE carries the same MAC-Address on the 5GHz WiFi.
