ath9k: Send AUTHORIZED event only for station mode

ATH_CHANCTX_EVENT_AUTHORIZED is required to trigger
the MCC scheduler when a station interface becomes
authorized. But, since the driver gets station state
notifications when the current operating mode is AP
too, make sure that we send ATH_CHANCTX_EVENT_AUTHORIZED
only when the interface is in station mode.

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