mac80211: split PS buffers into ACs

For uAPSD support we'll need to have per-AC PS
buffers. As this is a major undertaking, split
the buffers before really adding support for
uAPSD. This already makes some reference to the
uapsd_queues variable, but for now that will
never be non-zero.

Since book-keeping is complicated, also change
the logic for keeping a maximum of frames only
and allow 64 frames per AC (up from 128 for a
station).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/mac80211.h

@@ -109,6 +109,7 @@ enum ieee80211_ac_numbers {
 	IEEE80211_AC_BE		= 2,
 	IEEE80211_AC_BK		= 3,
 };
+#define IEEE80211_NUM_ACS	4
 
 /**
  * struct ieee80211_tx_queue_params - transmit queue configuration