mac80211: add debugfs file for last ack signal

Add a debugfs file showing the signal strength
of the ack frame that is received for the
currently sent tx packet

Signed-off-by: Saravana <saravanad@posedge.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -250,6 +250,7 @@ struct sta_ampdu_mlme {
  * @rx_dropped: number of dropped MPDUs from this STA
  * @last_signal: signal of last received frame from this STA
  * @avg_signal: moving average of signal of received frames from this STA
+ * @last_ack_signal: signal of last received Ack frame from this STA
  * @last_seq_ctrl: last received seq/frag number from this STA (per RX queue)
  * @tx_filtered_count: number of frames the hardware filtered for this STA
  * @tx_retry_failed: number of frames that failed retry
@@ -329,6 +330,7 @@ struct sta_info {
 	unsigned long rx_dropped;
 	int last_signal;
 	struct ewma avg_signal;
+	int last_ack_signal;
 	/* Plus 1 for non-QoS frames */
 	__le16 last_seq_ctrl[IEEE80211_NUM_TIDS + 1];