mac80211: mesh: drop frames appearing to be from us

If there are multiple mesh stations with the same MAC address,
they will both get confused and start throwing warnings.

Obviously in this case nothing can actually work anyway, so just
drop frames that look like they're from ourselves early on.
Reported-by: Gui Iribarren <gui@altermundi.net>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -3632,6 +3632,8 @@ static bool ieee80211_accept_frame(struct ieee80211_rx_data *rx)
 		}
 		return true;
 	case NL80211_IFTYPE_MESH_POINT:
+		if (ether_addr_equal(sdata->vif.addr, hdr->addr2))
+			return false;
 		if (multicast)
 			return true;
 		return ether_addr_equal(sdata->vif.addr, hdr->addr1);