mt76x02: initialize mutli bss mode when set up address

BSSID is not strtirct related with beaconing (for example we can have
2 STA vifs) and more related with MAC address, so initaize BSSID when
setting MAC address.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>