mac80211: rework TX filtered frame code

This reworks the code for TX filtered frames, splitting it out to
a new function to handle those cases, making the clear instruction
a flag and renaming a few things to be easier to understand and
less Atheros hardware specific. Finally, it also makes the comments
explain more.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 784ab76..cd4b1c1 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -228,7 +228,8 @@
 #define IEEE80211_TXCTL_NO_ACK		(1<<4) /* tell the low level not to
 						* wait for an ack */
 #define IEEE80211_TXCTL_RATE_CTRL_PROBE	(1<<5)
-#define IEEE80211_TXCTL_CLEAR_DST_MASK	(1<<6)
+#define IEEE80211_TXCTL_CLEAR_PS_FILT	(1<<6) /* clear powersave filter
+						* for destination station */
 #define IEEE80211_TXCTL_REQUEUE		(1<<7)
 #define IEEE80211_TXCTL_FIRST_FRAGMENT	(1<<8) /* this is a first fragment of
 						* the frame */