mt7603: pull the final rate index from the status descriptor

When doing rate probing, multiple frames might end up getting sent with
the probe rate, because of the way that rate probing is set up.
This race window is most visible with MCS rates and aggregation.

To improve rate control stats accuracy, pull the final tx rate from the
descriptor

Signed-off-by: Felix Fietkau <nbd@nbd.name>

mt7603_mac.c

@@ -917,6 +917,8 @@ static bool
 mt7603_fill_txs(struct mt7603_dev *dev, struct mt7603_sta *sta,
 		struct ieee80211_tx_info *info, __le32 *txs_data)
 {
+	int final_idx = 0;
+	u32 final_rate;
 	bool final_mpdu;
 	bool ack_timeout;
 	bool fixed_rate;
@@ -938,6 +940,7 @@ mt7603_fill_txs(struct mt7603_dev *dev, struct mt7603_sta *sta,
 	count = FIELD_GET(MT_TXS4_TX_COUNT, txs);
 
 	txs = le32_to_cpu(txs_data[0]);
+	final_rate = FIELD_GET(MT_TXS0_TX_RATE, txs);
 	ack_timeout = txs & MT_TXS0_ACK_TIMEOUT;
 
 	if (!(txs & MT_TXS0_ACK_ERROR_MASK)) {
@@ -998,9 +1001,13 @@ mt7603_fill_txs(struct mt7603_dev *dev, struct mt7603_sta *sta,
 		}
 
 		info->status.rates[i].count = cur_count;
+		final_idx = i;
 		count -= cur_count;
 	}
 
+	if (sta->rates[final_idx].flags & IEEE80211_TX_RC_MCS)
+		info->status.rates[final_idx].idx = final_rate & GENMASK(5, 0);
+
 	return true;
 }