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/netfilter/xt_u32.c b/net/netfilter/xt_u32.c
index f62797b..a95b5034 100644
--- a/net/netfilter/xt_u32.c
+++ b/net/netfilter/xt_u32.c
@@ -86,8 +86,7 @@
 	return true;
 }
 
-static bool u32_mt(const struct sk_buff *skb,
-		   const struct xt_action_param *par)
+static bool u32_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
 	const struct xt_u32 *data = par->matchinfo;
 	bool ret;