tools/gtp-tunnel: pass rc of gtp_add_tunnel

Don't exit with 0 if gtp_add_tunnel fails.

Change-Id: If11b1fb4487a96dcb7f24d95794fea4e36202203
diff --git a/tools/gtp-tunnel.c b/tools/gtp-tunnel.c
index b29e386..1fcdee7 100644
--- a/tools/gtp-tunnel.c
+++ b/tools/gtp-tunnel.c
@@ -77,6 +77,7 @@
 	uint32_t gtp_ifidx;
 	uint32_t gtp_version;
 	int optidx;
+	int ret;
 
 	if (argc < 7 || argc > 8) {
 		add_usage(argv[0]);
@@ -118,10 +119,10 @@
 	set_addr(argv[optidx++], true, t);
 	set_addr(argv[optidx++], false, t);
 
-	gtp_add_tunnel(genl_id, nl, t);
+	ret = gtp_add_tunnel(genl_id, nl, t);
 
 	gtp_tunnel_free(t);
-	return 0;
+	return ret;
 }
 
 static int