ath9k: Ensure xmit makes progress.

If the txq->axq_q is empty, the code was breaking out
of the tx_processq logic without checking to see if it should
transmit other queued AMPDU frames (txq->axq_acq).

This patches ensures ath_txq_schedule is called.

This needs review.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -2005,6 +2005,8 @@ static void ath_tx_processq(struct ath_softc *sc, struct ath_txq *txq)
 		spin_lock_bh(&txq->axq_lock);
 		if (list_empty(&txq->axq_q)) {
 			txq->axq_link = NULL;
+			if (sc->sc_flags & SC_OP_TXAGGR)
+				ath_txq_schedule(sc, txq);
 			spin_unlock_bh(&txq->axq_lock);
 			break;
 		}