mac80211: add get TID helper

Extracting the TID from the QOS header is common enough
to justify helper.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 5fe01f8..d13ba06 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -1324,8 +1324,7 @@ static void ieee80211_iface_work(struct work_struct *work)
 			mutex_lock(&local->sta_mtx);
 			sta = sta_info_get_bss(sdata, mgmt->sa);
 			if (sta) {
-				u16 tid = *ieee80211_get_qos_ctl(hdr) &
-						IEEE80211_QOS_CTL_TID_MASK;
+				u16 tid = ieee80211_get_tid(hdr);
 
 				__ieee80211_stop_rx_ba_session(
 					sta, tid, WLAN_BACK_RECIPIENT,