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/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index 4d90ed7..90c263d 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -110,6 +110,7 @@
 	struct sccp_source_reference real_ref;
 	struct sccp_source_reference patched_ref;
 	struct sccp_source_reference remote_ref;
+	int has_remote_ref;
 
 	/* GSM audio handling. That is 32 * multiplex + ts */
 	int crcx;