tools/gtp-tunnel: fix del usage

Change-Id: Iba5afd0cdb1588def3d865900ae02773dfd654e2
diff --git a/tools/gtp-tunnel.c b/tools/gtp-tunnel.c
index 513ff4a..1d8486c 100644
--- a/tools/gtp-tunnel.c
+++ b/tools/gtp-tunnel.c
@@ -120,7 +120,7 @@
 	uint32_t gtp_ifidx;
 
 	if (argc != 5) {
-		printf("%s add <gtp device> <version> <tid>\n",
+		printf("%s del <gtp device> <version> <tid>\n",
 			argv[0]);
 		return EXIT_FAILURE;
 	}