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/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index 75a4754..fa40f1f 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -1379,7 +1379,8 @@
 	 * connections present when one connection is removed from the
 	 * endpoint. */
 	llist_for_each_entry(conn_cleanup, &endp->conns, entry) {
-		conn_cleanup->priv = NULL;
+		if (conn_cleanup->priv == conn)
+			conn_cleanup->priv = NULL;
 	}
 }