ath9k_htc: Handle BSSID/AID for multiple interfaces

The AID and BSSID should be set in the HW only for the
first station interface or adhoc interface. Also, cancel
the ANI timer in stop() for multi-STA scenario. And finally
configure the HW beacon timers only for the first station
interface.

Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>