ath9k: fix powersave frame filtering/buffering in AP mode

This patch fixes a long standing issue of pending packets in the queue being
sent (and retransmitted many times) to sleeping stations.
This was made worse by aggregation through driver-internal retransmitting
of A-MDPU subframes.
Previously the hardware tx filter was cleared unconditionally for every
single packet - with this patch it uses the IEEE80211_TX_CTL_CLEAR_PS_FILT
for unaggregated frames.
A sta_notify driver op is added to stop aggregation for stations when they
enter powersave mode. Subframes stay buffered inside the driver, to ensure
that the BlockAck window keeps a sane state.
Since the driver uses software aggregation, the clearing of the tx filter
needs to be handled by the driver instead of mac80211 for aggregated frames.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/hw-ops.h b/drivers/net/wireless/ath/ath9k/hw-ops.h
index 22ee888..9dd90a8 100644
--- a/drivers/net/wireless/ath/ath9k/hw-ops.h
+++ b/drivers/net/wireless/ath/ath9k/hw-ops.h
@@ -122,6 +122,11 @@
 	ath9k_hw_ops(ah)->set11n_burstduration(ah, ds, burstDuration);
 }
 
+static inline void ath9k_hw_set_clrdmask(struct ath_hw *ah, void *ds, bool val)
+{
+	ath9k_hw_ops(ah)->set_clrdmask(ah, ds, val);
+}
+
 /* Private hardware call ops */
 
 /* PHY ops */