Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libipt_SNAT.c b/extensions/libipt_SNAT.c
index a18e36a..9460612 100644
--- a/extensions/libipt_SNAT.c
+++ b/extensions/libipt_SNAT.c
@@ -32,7 +32,7 @@
 IPTABLES_VERSION);
 }
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{ "to-source", 1, 0, '1' },
 	{ "random", 0, 0, '2' },
 	{ 0 }