ath9k: Fix PS mode operation to receive buffered broadcast/multicast frames

The previous implementation was moving back to NETWORK SLEEP state
immediately after receiving a Beacon frame. This means that we are
unlikely to receive all the buffered broadcast/multicast frames that
would be sent after DTIM Beacon frames. Fix this by parsing the Beacon
frame and remaining awake, if needed, to receive the buffered
broadcast/multicast frames. The last buffered frame will trigger the
move back into NETWORK SLEEP state.

If the last broadcast/multicast frame is not received properly (or if
the AP fails to send it), the next Beacon frame will work as a backup
trigger for returning into NETWORK SLEEP.

A new debug type, PS (debug=0x800 module parameter), is added to make
it easier to debug potential power save issues in the
future. Currently, this is only used for the Beacon frame and buffered
broadcast/multicast receiving.

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/debug.h b/drivers/net/wireless/ath/ath9k/debug.h
index 23298b9..db845cf 100644
--- a/drivers/net/wireless/ath/ath9k/debug.h
+++ b/drivers/net/wireless/ath/ath9k/debug.h
@@ -29,6 +29,7 @@
 	ATH_DBG_BEACON		= 0x00000100,
 	ATH_DBG_CONFIG		= 0x00000200,
 	ATH_DBG_FATAL		= 0x00000400,
+	ATH_DBG_PS		= 0x00000800,
 	ATH_DBG_ANY		= 0xffffffff
 };