qcacld-3.0: Report max MCS index 8 for VHT20

qcacld-2.0 to qcacld-3.0 propagation

Currently driver reports max MCS index 9 for VHT20, but cfg802.11
doesn't support such case, which leads to link speed null returned
to upper-layer.
Update the driver to report max MCS index 8 for VHT20.

Change-Id: I06c97db85d88decf418be602cb5f64135f61a686
CRs-Fixed: 1005141

core/hdd/src/wlan_hdd_stats.c

@@ -1864,8 +1864,15 @@ static int __wlan_hdd_cfg80211_get_station(struct wiphy *wiphy,
 					maxMCSIdx = 8;
 				else if (DATA_RATE_11AC_MAX_MCS_9 ==
 					   vhtMaxMcs) {
-					/* VHT20 is supporting 0~8 */
-					if (rate_flags & eHAL_TX_RATE_VHT20)
+					/*
+					 * IEEE_P802.11ac_2013.pdf page 325, 326
+					 * - MCS9 is valid for VHT20 when
+					 *   Nss = 3 or Nss = 6
+					 * - MCS9 is not valid for VHT20 when
+					 *   Nss = 1,2,4,5,7,8
+					 */
+					if ((rate_flags & eHAL_TX_RATE_VHT20) &&
+					     (nss != 3 && nss != 6))
 						maxMCSIdx = 8;
 					else
 						maxMCSIdx = 9;
@@ -1973,6 +1980,18 @@ static int __wlan_hdd_cfg80211_get_station(struct wiphy *wiphy,
 				maxSpeedMCS = 1;
 				maxMCSIdx =
 				  pAdapter->hdd_stats.ClassA_stat.mcs_index;
+				/*
+				 * IEEE_P802.11ac_2013.pdf page 325, 326
+				 * - MCS9 is valid for VHT20 when
+				 *   Nss = 3 or Nss = 6
+				 * - MCS9 is not valid for VHT20 when
+				 *   Nss = 1,2,4,5,7,8
+				 */
+				if ((rate_flags & eHAL_TX_RATE_VHT20) &&
+				    (maxMCSIdx > 8) &&
+				    (nss != 3 && nss != 6)) {
+					maxMCSIdx = 8;
+				}
 			}
 		}