ath9k: Use mac80211 for multicast power save buffering

Replace the internal ath9k implementation of multicast/broadcast frame
power save buffering (AP mode) in ath9k with use of mac80211
ieee80211_get_buffered_bc() mechanism. This removes quite a bit of
duplicated functionality and simplifies the driver part.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath9k/ath9k.h b/drivers/net/wireless/ath9k/ath9k.h
index 18028a3..841893b 100644
--- a/drivers/net/wireless/ath9k/ath9k.h
+++ b/drivers/net/wireless/ath9k/ath9k.h
@@ -144,6 +144,7 @@
 #define ATH9K_TXDESC_EXT_AND_CTL	0x0080
 #define ATH9K_TXDESC_VMF		0x0100
 #define ATH9K_TXDESC_FRAG_IS_ON 	0x0200
+#define ATH9K_TXDESC_CAB		0x0400
 
 #define ATH9K_RXDESC_INTREQ		0x0020