ath9k: Dont update rate control for every AMPDU

Update the rate control only with the tx status of first
AMPDU of an aggregation. This patch fixes frequent drops
in throughput.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath9k/xmit.c b/drivers/net/wireless/ath9k/xmit.c
index 50d4105..dad81a9 100644
--- a/drivers/net/wireless/ath9k/xmit.c
+++ b/drivers/net/wireless/ath9k/xmit.c
@@ -950,6 +950,7 @@
 	struct ieee80211_tx_info *tx_info = IEEE80211_SKB_CB(skb);
 	struct ath_tx_info_priv *tx_info_priv = ATH_TX_INFO_PRIV(tx_info);
 
+	tx_info_priv->update_rc = false;
 	if (ds->ds_txstat.ts_status & ATH9K_TXERR_FILT)
 		tx_info->flags |= IEEE80211_TX_STAT_TX_FILTERED;
 
@@ -960,6 +961,7 @@
 			       sizeof(tx_info_priv->tx));
 			tx_info_priv->n_frames = bf->bf_nframes;
 			tx_info_priv->n_bad_frames = nbad;
+			tx_info_priv->update_rc = true;
 		}
 	}
 }