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/net/mac80211/util.c b/net/mac80211/util.c
index 9d255a2..89c1e5b 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1793,3 +1793,11 @@
 	}
 	return 0;
 }
+
+int ieee80211_ave_rssi(struct ieee80211_vif *vif)
+{
+	struct ieee80211_sub_if_data *sdata = vif_to_sdata(vif);
+	struct ieee80211_if_managed *ifmgd = &sdata->u.mgd;
+
+	return ifmgd->ave_beacon_signal;
+}