netfilter: x_tables: make sure e->next_offset covers remaining blob size

Otherwise this function may read data beyond the ruleset blob.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
struct arpt_entry *arpt_next_entry(const struct arpt_entry *entry)
{
	return (void *)entry + entry->next_offset;
}

struct arpt_entry *arpt_next_entry(const struct arpt_entry *entry)
{
	return (void *)entry + entry->next_offset;
}
