fix infinite recursion with routing by global title

We don't implement routing by global title address.
When processing an SCCP message which is routed by global title,
don't recurs indefinitely until the stack is exhausted.
Instead, return an error with cause SUBSYSTEM_FAILURE, which we
also do in other routing failure cases.

Change-Id: I24621e77ffc979bc337775f9c6a4ad9a9068625a
Related: OS#2666

src/sccp_scrc.c

@@ -279,8 +279,15 @@ static int scrc_translate_node_9(struct osmo_sccp_instance *inst,
 	    translated.ri != OSMO_SCCP_RI_SSN_IP) {
 		/* TODO: GT Routing */
 		LOGP(DLSCCP, LOGL_NOTICE, "GT Routing not implemented yet\n");
+#if 1
+		/* Prevent endless recursion, see OS#2666. */
+		sccp_sclc_rx_scrc_rout_fail(inst, xua,
+			SCCP_RETURN_CAUSE_SUBSYSTEM_FAILURE);
+		return 0;
+#else
 		/* Node 7 (Sheet 5) */
 		return scrc_node_7(inst, xua, called);
+#endif
 	}
 
 	/* Check DPC resultant from GT translation */