ramips: work around duplicate MAC address on U6 Lite

ramips: work around duplicate MAC address on U6 Lite

The UniFi 6 Lite has two MAC addresses for the 2.4 and 5GHz radio in
it's EEPROM partition.

On my unit these are

F4 92 BF A0 BB 6F
F6 92 BF A0 BB 6F

The problem with these is that mac80211 increases the first octet by
2, which leads to conflicting MAC addresses between radios.

Work around this problem for now by increasing the last octet by 1 on
the 5 GHz radio.

Ubiquiti increases the last octet by 2 for each subsequent VAP created
per radio. Ideally we should do the same, however this functionality is
currently lacking from mac80211.

Signed-off-by: David Bauer <mail@david-bauer.net>