Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libxt_tcp.c b/extensions/libxt_tcp.c
index da4922b..e5db637 100644
--- a/extensions/libxt_tcp.c
+++ b/extensions/libxt_tcp.c
@@ -27,7 +27,7 @@
 IPTABLES_VERSION);
 }
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{ "source-port", 1, 0, '1' },
 	{ "sport", 1, 0, '1' }, /* synonym */
 	{ "destination-port", 1, 0, '2' },