mt7601u: move mt7601u_set_macaddr in mac related code

Remove static qualifier from mt7601u_set_macaddr routine and move it
in mac related code in order to be used to properly support vif with
different mac address respect to the default one

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>