ath5k: fix setup for CAB queue

The beacon sent gating doesn't seem to work with any combination
of flags.  Thus, buffered frames tend to stay buffered forever,
using up tx descriptors.

Instead, use the DBA gating and hold transmission of the buffered
frames until 80% of the beacon interval has elapsed using the ready
time.  This fixes the following error in AP mode:

   ath5k phy0: no further txbuf available, dropping packet

Add a comment to acknowledge that this isn't the best solution.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/qcu.c b/drivers/net/wireless/ath/ath5k/qcu.c
index abe36c0..9122a85 100644
--- a/drivers/net/wireless/ath/ath5k/qcu.c
+++ b/drivers/net/wireless/ath/ath5k/qcu.c
@@ -408,12 +408,13 @@
 			break;
 
 		case AR5K_TX_QUEUE_CAB:
+			/* XXX: use BCN_SENT_GT, if we can figure out how */
 			AR5K_REG_ENABLE_BITS(ah, AR5K_QUEUE_MISC(queue),
-				AR5K_QCU_MISC_FRSHED_BCN_SENT_GT |
+				AR5K_QCU_MISC_FRSHED_DBA_GT |
 				AR5K_QCU_MISC_CBREXP_DIS |
 				AR5K_QCU_MISC_CBREXP_BCN_DIS);
 
-			ath5k_hw_reg_write(ah, ((AR5K_TUNE_BEACON_INTERVAL -
+			ath5k_hw_reg_write(ah, ((tq->tqi_ready_time -
 				(AR5K_TUNE_SW_BEACON_RESP -
 				AR5K_TUNE_DMA_BEACON_RESP) -
 				AR5K_TUNE_ADDITIONAL_SWBA_BACKOFF) * 1024) |