Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libipt_NETMAP.c b/extensions/libipt_NETMAP.c
index 302448f..ef06e01 100644
--- a/extensions/libipt_NETMAP.c
+++ b/extensions/libipt_NETMAP.c
@@ -13,7 +13,7 @@
 
 #define MODULENAME "NETMAP"
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{ "to", 1, 0, '1' },
 	{ 0 }
 };