fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_esp.c b/extensions/libxt_esp.c
index e5b5eaa..f37c088 100644
--- a/extensions/libxt_esp.c
+++ b/extensions/libxt_esp.c
@@ -20,7 +20,7 @@
 
 static const struct option esp_opts[] = {
 	{ "espspi", 1, NULL, '1' },
-	{ }
+	{ .name = NULL }
 };
 
 static u_int32_t