nat: Only close connections that were fully connected

Remember that we have seen a CC and have a valid destination
local reference now and only send a fake RLC to the MSC when
we had connections in this state.
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index d5ed751..5284427 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -444,7 +444,8 @@
 		if (sccp_patch->bsc != connection)
 			continue;
 
-		nat_send_rlsd(sccp_patch);
+		if (sccp_patch->has_remote_ref)
+			nat_send_rlsd(sccp_patch);
 		sccp_connection_destroy(sccp_patch);
 	}