ath9k: built-in rate control A-MPDU fix

This patch attempts to ensure that ath9k's built-in rate control algorithm
does not rely on the value of the ampdu_len and ampdu_ack_len tx status
fields unless the IEEE80211_TX_STAT_AMPDU flag is set.

This patch has not been tested.

Cc: <stable@kernel.org>
Signed-off-by: Björn Smedman <bjorn.smedman@venatech.se>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/rc.c

@@ -1375,6 +1375,12 @@ static void ath_tx_status(void *priv, struct ieee80211_supported_band *sband,
 	if (tx_info->flags & IEEE80211_TX_STAT_TX_FILTERED)
 		return;
 
+	if (!(tx_info->flags & IEEE80211_TX_STAT_AMPDU)) {
+		tx_info->status.ampdu_ack_len =
+			(tx_info->flags & IEEE80211_TX_STAT_ACK ? 1 : 0);
+		tx_info->status.ampdu_len = 1;
+	}
+
 	/*
 	 * If an underrun error is seen assume it as an excessive retry only
 	 * if max frame trigger level has been reached (2 KB for singel stream,