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_sccp.c b/openbsc/src/nat/bsc_sccp.c
index c422cc5..3449531 100644
--- a/openbsc/src/nat/bsc_sccp.c
+++ b/openbsc/src/nat/bsc_sccp.c
@@ -141,6 +141,7 @@
 	}
 
 	sccp->remote_ref = *parsed->src_local_ref;
+	sccp->has_remote_ref = 1;
 	LOGP(DNAT, LOGL_DEBUG, "Updating 0x%x to remote 0x%x on %p\n",
 	     sccp_src_ref_to_int(&sccp->patched_ref),
 	     sccp_src_ref_to_int(&sccp->remote_ref), sccp->bsc);