fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libip6t_icmp6.c b/extensions/libip6t_icmp6.c
index febf523..8c9653f 100644
--- a/extensions/libip6t_icmp6.c
+++ b/extensions/libip6t_icmp6.c
@@ -86,7 +86,7 @@
 
 static const struct option icmp6_opts[] = {
 	{ "icmpv6-type", 1, NULL, '1' },
-	{ }
+	{ .name = NULL }
 };
 
 static void