mac80211: only respond to probe request with mesh ID

Previously, the mesh STA responds to probe request from legacy STA
but now it will only respond to legacy STA if the legacy STA does include
the specific mesh ID or wildcard mesh ID in the probe request.

The iw patch "iw: scan using meshid" can be used either by legacy STA
or by mesh STA to do active scanning by inserting the mesh ID in the
probe request frame.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@cozybit.com>
Acked-by: Thomas Pedersen <thomas@cozybit.com>
Acked-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mesh.c

@@ -832,6 +832,9 @@ ieee80211_mesh_rx_probe_req(struct ieee80211_sub_if_data *sdata,
 
 	ieee802_11_parse_elems(pos, len - baselen, false, &elems);
 
+	if (!elems.mesh_id)
+		return;
+
 	/* 802.11-2012 10.1.4.3.2 */
 	if ((!ether_addr_equal(mgmt->da, sdata->vif.addr) &&
 	     !is_broadcast_ether_addr(mgmt->da)) ||