mac80211: Simplify locking in ieee80211_sta_tear_down_BA_sessions()

Simplify the locking in  ieee80211_sta_tear_down_BA_sessions() and
lock sta->ampdu_mlme.mtx over the entire function instead of
locking/unlocking it for each TID etc.
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ht.c

@@ -290,13 +290,15 @@ void ieee80211_sta_tear_down_BA_sessions(struct sta_info *sta,
 {
 	int i;
 
+	mutex_lock(&sta->ampdu_mlme.mtx);
 	for (i = 0; i <  IEEE80211_NUM_TIDS; i++) {
-		__ieee80211_stop_tx_ba_session(sta, i, reason);
-		__ieee80211_stop_rx_ba_session(sta, i, WLAN_BACK_RECIPIENT,
+		___ieee80211_stop_tx_ba_session(sta, i, reason);
+		___ieee80211_stop_rx_ba_session(sta, i, WLAN_BACK_RECIPIENT,
 						WLAN_REASON_QSTA_LEAVE_QBSS,
 						reason != AGG_STOP_DESTROY_STA &&
 						reason != AGG_STOP_PEER_REQUEST);
 	}
+	mutex_unlock(&sta->ampdu_mlme.mtx);
 
 	/* stopping might queue the work again - so cancel only afterwards */
 	cancel_work_sync(&sta->ampdu_mlme.work);