mgw: Release endpoint after last conn times out

Otherwise some state is kept, like the previous CallId, which may then
provoke issues next time the endpoint is to be used.

Change-Id: I3ac4f4542c1c8c877127c64acce6c82b458f697f
diff --git a/include/osmocom/mgcp/mgcp_endp.h b/include/osmocom/mgcp/mgcp_endp.h
index 14cae25..8d19b44 100644
--- a/include/osmocom/mgcp/mgcp_endp.h
+++ b/include/osmocom/mgcp/mgcp_endp.h
@@ -139,3 +139,5 @@
 struct mgcp_endpoint *mgcp_endp_by_name(int *cause, const char *epname,
 					struct mgcp_config *cfg);
 bool mgcp_endp_avail(struct mgcp_endpoint *endp);
+void mgcp_endp_add_conn(struct mgcp_endpoint *endp, struct mgcp_conn *conn);
+void mgcp_endp_remove_conn(struct mgcp_endpoint *endp, struct mgcp_conn *conn);