nat: Free the endpoint when we get an empty CI.

In case the BSC is sending us an empty/unused CI we have
a bug, but for now let us free the endpoint and figure out
which response we are getting.

openbsc/src/nat/bsc_mgcp_utils.c

@@ -314,6 +314,13 @@ void bsc_mgcp_forward(struct bsc_connection *bsc, struct msgb *msg)
 	}
 
 	endp->ci = bsc_mgcp_extract_ci((const char *) msg->l2h);
+	if (endp->ci == CI_UNUSED) {
+		LOGP(DMGCP, LOGL_ERROR, "No CI, freeing endpoint 0x%x\n",
+			ENDPOINT_NUMBER(endp));
+		bsc_mgcp_free_endpoint(bsc->nat, ENDPOINT_NUMBER(endp));
+		mgcp_free_endp(endp);
+		return;
+	}
 
 	/* free some stuff */
 	talloc_free(bsc_endp->transaction_id);