mac80211: max_tp_rate2 management of minstrel_ht

I noticed a possible issue in the max_tp_rate2 management of
minstrel_ht. In particular, if we look up just among max_tp_rate2 of
each group it will be possible that the selected rate will not be the
mcs with second maximum throughput. I wrote this simple patch.

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rc80211_minstrel_ht.c

@@ -281,6 +281,8 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 
 		mr = minstrel_get_ratestats(mi, mg->max_tp_rate);
 		if (cur_tp < mr->cur_tp) {
+			mi->max_tp_rate2 = mi->max_tp_rate;
+			cur_tp2 = cur_tp;
 			mi->max_tp_rate = mg->max_tp_rate;
 			cur_tp = mr->cur_tp;
 		}