Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libip6t_ipv6header.c b/extensions/libip6t_ipv6header.c
index 858e029..4dab33f 100644
--- a/extensions/libip6t_ipv6header.c
+++ b/extensions/libip6t_ipv6header.c
@@ -148,7 +148,7 @@
 	IPTABLES_VERSION);
 }
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{ "header", 1, 0, '1' },
 	{ "soft", 0, 0, '2' },
 	{ 0 }