{nl,cfg,mac}80211: Implement RSSI threshold for mesh peering

Mesh peer links are established only if average rssi of the peer
candidate satisfies the threshold. This is not in 802.11s specification
but was requested by David Fulgham, an open80211s user. This is a way to avoid
marginal peer links with stations that are barely within range.

This patch adds a new mesh configuration parameter, mesh_rssi_threshold. This
feature is supported only for hardwares that report signal in dBm.

Signed-off-by: Ashok Nagarajan <ashok@cozybit.com>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 0178c74..b4e015c 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -809,6 +809,7 @@
 	 * Still keeping the same nomenclature to be in sync with the spec. */
 	bool  dot11MeshGateAnnouncementProtocol;
 	bool dot11MeshForwarding;
+	s32 rssi_threshold;
 };
 
 /**