wifi: mt76: connac: update nss calculation in txs

The hardware reports the number of transmitting antennas not the actual
number of spatial streams

Co-developed-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Evelyn Tsai <evelyn.tsai@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c

@@ -567,7 +567,7 @@ bool mt76_connac2_mac_fill_txs(struct mt76_dev *dev, struct mt76_wcid *wcid,
 	struct mt76_phy *mphy;
 	struct rate_info rate = {};
 	bool cck = false;
-	u32 txrate, txs, mode;
+	u32 txrate, txs, mode, stbc;
 
 	txs = le32_to_cpu(txs_data[0]);
 
@@ -587,6 +587,10 @@ bool mt76_connac2_mac_fill_txs(struct mt76_dev *dev, struct mt76_wcid *wcid,
 
 	rate.mcs = FIELD_GET(MT_TX_RATE_IDX, txrate);
 	rate.nss = FIELD_GET(MT_TX_RATE_NSS, txrate) + 1;
+	stbc = FIELD_GET(MT_TX_RATE_STBC, txrate);
+
+	if (stbc && rate.nss > 1)
+		rate.nss >>= 1;
 
 	if (rate.nss - 1 < ARRAY_SIZE(stats->tx_nss))
 		stats->tx_nss[rate.nss - 1]++;