ath9k: Fix bug in handling single stream stations

AP mode currently sets up the dual stream capability
for all stations. This patch fixes it by checking if the
associated station supports dual stream MCS rates (8-15).
We would disregard any MCS rates above 15, since Atheros
HW supports only 0..15 rates currently, and can't receive
at rates > 15 anyway.

Signed-off-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath9k/rc.c b/drivers/net/wireless/ath9k/rc.c
index 28d69da..74bc4e6 100644
--- a/drivers/net/wireless/ath9k/rc.c
+++ b/drivers/net/wireless/ath9k/rc.c
@@ -1470,16 +1470,18 @@
 		ath_rc_priv->ht_cap);
 }
 
-static u8 ath_rc_build_ht_caps(struct ath_softc *sc, bool is_ht, bool is_cw40,
-			       bool is_sgi40)
+static u8 ath_rc_build_ht_caps(struct ath_softc *sc, struct ieee80211_sta *sta,
+			       bool is_cw40, bool is_sgi40)
 {
 	u8 caps = 0;
 
-	if (is_ht) {
+	if (sta->ht_cap.ht_supported) {
 		caps = WLAN_RC_HT_FLAG;
 		if (sc->sc_ah->caps.tx_chainmask != 1 &&
-		    ath9k_hw_getcapability(sc->sc_ah, ATH9K_CAP_DS, 0, NULL))
-			caps |= WLAN_RC_DS_FLAG;
+		    ath9k_hw_getcapability(sc->sc_ah, ATH9K_CAP_DS, 0, NULL)) {
+			if (sta->ht_cap.mcs.rx_mask[1])
+				caps |= WLAN_RC_DS_FLAG;
+		}
 		if (is_cw40)
 			caps |= WLAN_RC_40_FLAG;
 		if (is_sgi40)
@@ -1626,8 +1628,7 @@
 		rate_table = sc->cur_rate_table;
 	}
 
-	ath_rc_priv->ht_cap = ath_rc_build_ht_caps(sc, sta->ht_cap.ht_supported,
-						   is_cw40, is_sgi40);
+	ath_rc_priv->ht_cap = ath_rc_build_ht_caps(sc, sta, is_cw40, is_sgi40);
 	ath_rc_init(sc, priv_sta, sband, sta, rate_table);
 }
 
@@ -1661,8 +1662,7 @@
 			rate_table = ath_choose_rate_table(sc, sband->band,
 						   sta->ht_cap.ht_supported,
 						   oper_cw40);
-			ath_rc_priv->ht_cap = ath_rc_build_ht_caps(sc,
-						   sta->ht_cap.ht_supported,
+			ath_rc_priv->ht_cap = ath_rc_build_ht_caps(sc, sta,
 						   oper_cw40, oper_sgi40);
 			ath_rc_init(sc, priv_sta, sband, sta, rate_table);