rt2x00: pause almost full queue early

Do not drop &queue->tx_lock and acquire it again to pause queue when
available entries are below the threshold.

Patch should mitigate problem of frequently printed errors:
"Error - Dropping frame due to full tx queue"
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Tested-by: Enrico Mioso@gmail.com
Tested-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ralink/rt2x00/rt2x00mac.c

@@ -152,16 +152,6 @@ void rt2x00mac_tx(struct ieee80211_hw *hw,
 	if (unlikely(rt2x00queue_write_tx_frame(queue, skb, control->sta, false)))
 		goto exit_fail;
 
-	/*
-	 * Pausing queue has to be serialized with rt2x00lib_txdone(). Note
-	 * we should not use spin_lock_bh variant as bottom halve was already
-	 * disabled before ieee80211_xmit() call.
-	 */
-	spin_lock(&queue->tx_lock);
-	if (rt2x00queue_threshold(queue))
-		rt2x00queue_pause_queue(queue);
-	spin_unlock(&queue->tx_lock);
-
 	return;
 
  exit_fail:

drivers/net/wireless/ralink/rt2x00/rt2x00queue.c

@@ -715,6 +715,14 @@ int rt2x00queue_write_tx_frame(struct data_queue *queue, struct sk_buff *skb,
 	rt2x00queue_kick_tx_queue(queue, &txdesc);
 
 out:
+	/*
+	 * Pausing queue has to be serialized with rt2x00lib_txdone(), so we
+	 * do this under queue->tx_lock. Bottom halve was already disabled
+	 * before ieee80211_xmit() call.
+	 */
+	if (rt2x00queue_threshold(queue))
+		rt2x00queue_pause_queue(queue);
+
 	spin_unlock(&queue->tx_lock);
 	return ret;
 }