ath5k: use common curbssid, bssidmask and macaddr

The ah_sta_id was really being used as the macaddr.
ath5k still does not use the association ID now passed
up by mac80211, that can be fixed later.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>