iwlwifi: mvm: clear csa countdown when AP is stopped

The csa_countdown flag was not cleared when the AP is stopped.
As a result, if the AP was stopped after csa_countdown had started,
all the folowing channel switch commands would fail.
Fix that by clearing the csa_countdown flag when the AP is stopped.

Cc: <stable@vger.kernel.org> [3.17+]
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/iwlwifi/mvm/mac80211.c

@@ -2388,6 +2388,7 @@ static void iwl_mvm_stop_ap_ibss(struct ieee80211_hw *hw,
 		iwl_mvm_remove_time_event(mvm, mvmvif,
 					  &mvmvif->time_event_data);
 		RCU_INIT_POINTER(mvm->csa_vif, NULL);
+		mvmvif->csa_countdown = false;
 	}
 
 	if (rcu_access_pointer(mvm->csa_tx_blocked_vif) == vif) {