Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libipt_realm.c b/extensions/libipt_realm.c
index 445bcc8..0b11457 100644
--- a/extensions/libipt_realm.c
+++ b/extensions/libipt_realm.c
@@ -25,7 +25,7 @@
 "\n", IPTABLES_VERSION);
 }
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{ "realm", 1, 0, '1' },
 	{0}
 };