carl9170: fix AMPDU TX_CTL_REQ_TX_STATUS handling

Previously the driver did not care if TX_CTL_REQ_TX_STATUS
was set on aggregated frames or not and it would silently
drop successfully sent frames if possible [much like:
"no news is good news!"].

But, TX_CTL_REQ_TX_STATUS was invented for a reason and
no tx status report should ever be dropped if it is set.
Reported-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NChristian Lamparter <chunkeey@googlemail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/tx.c

@@ -296,7 +296,8 @@ static void carl9170_tx_release(struct kref *ref)
 			super = (void *)skb->data;
 			txinfo->status.ampdu_len = super->s.rix;
 			txinfo->status.ampdu_ack_len = super->s.cnt;
-		} else if (txinfo->flags & IEEE80211_TX_STAT_ACK) {
+		} else if ((txinfo->flags & IEEE80211_TX_STAT_ACK) &&
+			   !(txinfo->flags & IEEE80211_TX_CTL_REQ_TX_STATUS)) {
 			/*
 			 * drop redundant tx_status reports:
 			 *
@@ -308,15 +309,17 @@ static void carl9170_tx_release(struct kref *ref)
 			 *
 			 * 3. minstrel_ht is picky, it only accepts
 			 *    reports of frames with the TX_STATUS_AMPDU flag.
+			 *
+			 * 4. mac80211 is not particularly interested in
+			 *    feedback either [CTL_REQ_TX_STATUS not set]
 			 */
 
 			dev_kfree_skb_any(skb);
 			return;
 		} else {
 			/*
-			 * Frame has failed, but we want to keep it in
-			 * case it was lost due to a power-state
-			 * transition.
+			 * Either the frame transmission has failed or
+			 * mac80211 requested tx status.
 			 */
 		}
 	}