nat: Clear the connection on a DLCX

We can forget about the timeslot/multiplex when getting
the DLCX. This way we make room for the next connection
that might need to reuse this address.
diff --git a/openbsc/src/nat/bsc_mgcp_utils.c b/openbsc/src/nat/bsc_mgcp_utils.c
index abfadb8..0e34e68 100644
--- a/openbsc/src/nat/bsc_mgcp_utils.c
+++ b/openbsc/src/nat/bsc_mgcp_utils.c
@@ -178,6 +178,7 @@
 		}
 	} else if (state == MGCP_ENDP_DLCX) {
 		/* we will free the endpoint now in case the BSS does not respond */
+		bsc_mgcp_clear(sccp);
 		bsc_endp->pending_delete = 1;
 		mgcp_free_endp(mgcp_endp);
 	}