ranap: log ranap iu event type name instead of number

Change-Id: If66e9d5989b46abe01855a5c1183d567d358abeb
diff --git a/src/sgsn/gprs_ranap.c b/src/sgsn/gprs_ranap.c
index 1f8ed97..2d2d3aa 100644
--- a/src/sgsn/gprs_ranap.c
+++ b/src/sgsn/gprs_ranap.c
@@ -120,7 +120,8 @@
 
 	mm = sgsn_mm_ctx_by_ue_ctx(ctx);
 	if (!mm) {
-		LOGIUP(ctx, LOGL_NOTICE, "Cannot find mm ctx for IU event %d\n", type);
+		LOGIUP(ctx, LOGL_NOTICE, "Cannot find mm ctx for IU event %s\n",
+		       ranap_iu_event_type_str(type));
 		ranap_iu_free_ue(ctx);
 		return rc;
 	}