ath9k: Reconfigure VIF state properly

When an interface in AP or P2P-GO mode is removed,
check whether a station interface is already present and
reconfigure the beacon timers etc. properly if it's
associated.

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