atheros/ath9k: move macaddr, curaid, curbssid and bssidmask to common

These are common amongst ath9k and ath5k, so put them into the
common structure and make ath9k to use it. ar9170 can use macaddr,
and curbssid. We'll change ath5k and ar9170 separately.

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