rt2x00: Implement tx_frames_pending mac80211 callback function.

Implementing this callback function will cause mac80211 refrain from
going to powersave state when there are still untransmitted TX frames
in the queues.
This would exactly mimic the behaviour of the legacy vendor driver which
also doesn't go in powersave mode if there are still TX frames that are not
transmitted.
This should make powersaving and rt2x00 a better couple.

Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt2x00.h b/drivers/net/wireless/rt2x00/rt2x00.h
index c446db6..db435ab 100644
--- a/drivers/net/wireless/rt2x00/rt2x00.h
+++ b/drivers/net/wireless/rt2x00/rt2x00.h
@@ -1276,6 +1276,7 @@
 int rt2x00mac_get_antenna(struct ieee80211_hw *hw, u32 *tx_ant, u32 *rx_ant);
 void rt2x00mac_get_ringparam(struct ieee80211_hw *hw,
 			     u32 *tx, u32 *tx_max, u32 *rx, u32 *rx_max);
+bool rt2x00mac_tx_frames_pending(struct ieee80211_hw *hw);
 
 /*
  * Driver allocation handlers.