mac80211: handle aggregation session timeout on fast-xmit path

The conversion to the fast-xmit path lost proper aggregation session
timeout handling - the last_tx wasn't set on that path and the timer
would therefore incorrectly tear down the session periodically (with
those drivers/rate control algorithms that have a timeout.)

In case of iwlwifi, this was every 5 seconds and caused significant
throughput degradation.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -2719,9 +2719,12 @@ static bool ieee80211_xmit_fast(struct ieee80211_sub_if_data *sdata,
 	if (hdr->frame_control & cpu_to_le16(IEEE80211_STYPE_QOS_DATA)) {
 		tid = skb->priority & IEEE80211_QOS_CTL_TAG1D_MASK;
 		tid_tx = rcu_dereference(sta->ampdu_mlme.tid_tx[tid]);
-		if (tid_tx &&
-		    !test_bit(HT_AGG_STATE_OPERATIONAL, &tid_tx->state))
+		if (tid_tx) {
+			if (!test_bit(HT_AGG_STATE_OPERATIONAL, &tid_tx->state))
 				return false;
+			if (tid_tx->timeout)
+				tid_tx->last_tx = jiffies;
+		}
 	}
 
 	/* after this point (skb is modified) we cannot return false */