mgw: mgcp_protocol: assert freeing last conn allows creating new conn

Change-Id: Ib8c9089a7f04bc67e5bdfb1148cfc603f0e17bb7

src/libosmo-mgcp/mgcp_protocol.c

@@ -976,6 +976,7 @@ mgcp_header_done:
 			 * room by blindly tossing the oldest of the two two
 			 * connections */
 			mgcp_endp_free_conn_oldest(endp);
+			OSMO_ASSERT(!mgcp_endp_is_full(endp));
 		} else {
 			/* There is no more room for a connection, leave
 			 * everything as it is and return with an error */