mac80211: Copy tx'ed beacons to monitor mode

When debugging wireless powersave issues on the AP side it's quite helpful
to see our own beacons that are transmitted by the hardware/driver. However,
this is not that easy since beacons don't pass through the regular TX queues.

Preferably drivers would call ieee80211_tx_status also for tx'ed beacons
but that's not always possible. Hence, just send a copy of each beacon
generated by ieee80211_beacon_get_tim to monitor devices when they are
getting fetched by the driver.

Also add a HW flag IEEE80211_HW_BEACON_TX_STATUS that can be used by
drivers to indicate that they report TX status for beacons.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
(with a fix from Christian Lamparted rolled in)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -1898,6 +1898,9 @@ struct ieee80211_txq {
  * @IEEE80211_HW_SUPPORTS_AMSDU_IN_AMPDU: The driver supports receiving A-MSDUs
  *	within A-MPDU.
  *
+ * @IEEE80211_HW_BEACON_TX_STATUS: The device/driver provides TX status
+ *	for sent beacons.
+ *
  * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
  */
 enum ieee80211_hw_flags {
@@ -1932,6 +1935,7 @@ enum ieee80211_hw_flags {
 	IEEE80211_HW_SINGLE_SCAN_ON_ALL_BANDS,
 	IEEE80211_HW_TDLS_WIDER_BW,
 	IEEE80211_HW_SUPPORTS_AMSDU_IN_AMPDU,
+	IEEE80211_HW_BEACON_TX_STATUS,
 
 	/* keep last, obviously */
 	NUM_IEEE80211_HW_FLAGS