mac80211: Update last_tx_rate only for data frames

The last_tx_rate field was also updated for non-data frames that are
often sent with a lower rate (for example management frames at 1 Mbps).
This is confusing when the data rate is actually much higher.

Hence, only update the last_tx_rate field with tx rate information
gathered from last data frames.

If the rate control algorithm filled in txrc.reported_rate we don't need
to verify this information.

Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -666,10 +666,11 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
 	if (unlikely(info->control.rates[0].idx < 0))
 		return TX_DROP;
 
-	if (txrc.reported_rate.idx < 0)
+	if (txrc.reported_rate.idx < 0) {
 		txrc.reported_rate = info->control.rates[0];
-
-	if (tx->sta)
+		if (tx->sta && ieee80211_is_data(hdr->frame_control))
+			tx->sta->last_tx_rate = txrc.reported_rate;
+	} else if (tx->sta)
 		tx->sta->last_tx_rate = txrc.reported_rate;
 
 	if (unlikely(!info->control.rates[0].count))