mac80211: add function retrieve average rssi

Add utility function to provide the average rssi per vif

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index eff00e6d..bebd89f 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -3801,4 +3801,7 @@
 
 int ieee80211_add_ext_srates_ie(struct ieee80211_vif *vif,
 				struct sk_buff *skb, bool need_basic);
+
+int ieee80211_ave_rssi(struct ieee80211_vif *vif);
+
 #endif /* MAC80211_H */