Make the option structures const.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libxt_pkttype.c b/extensions/libxt_pkttype.c
index 81cd943..3732034 100644
--- a/extensions/libxt_pkttype.c
+++ b/extensions/libxt_pkttype.c
@@ -64,7 +64,7 @@
 	print_types();
 }
 
-static struct option opts[] = {
+static const struct option opts[] = {
 	{"pkt-type", 1, 0, '1'},
 	{0}
 };