netfilter: xtables: deconstify struct xt_action_param for matches

In future, layer-3 matches will be an xt module of their own, and
need to set the fragoff and thoff fields. Adding more pointers would
needlessy increase memory requirements (esp. so for 64-bit, where
pointers are wider).

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/net/ipv6/netfilter/ip6t_eui64.c b/net/ipv6/netfilter/ip6t_eui64.c
index 2fd2be1..f32fce3 100644
--- a/net/ipv6/netfilter/ip6t_eui64.c
+++ b/net/ipv6/netfilter/ip6t_eui64.c
@@ -20,7 +20,7 @@
 MODULE_AUTHOR("Andras Kis-Szabo <kisza@sch.bme.hu>");
 
 static bool
-eui64_mt6(const struct sk_buff *skb, const struct xt_action_param *par)
+eui64_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	unsigned char eui64[8];