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>
static void __exit ip_tables_fini(void)
{
	nf_unregister_sockopt(&ipt_sockopts);

	xt_unregister_matches(ipt_builtin_mt, ARRAY_SIZE(ipt_builtin_mt));
	xt_unregister_targets(ipt_builtin_tg, ARRAY_SIZE(ipt_builtin_tg));
	unregister_pernet_subsys(&ip_tables_net_ops);
}

static void __exit ip_tables_fini(void)
{
	nf_unregister_sockopt(&ipt_sockopts);

	xt_unregister_matches(ipt_builtin_mt, ARRAY_SIZE(ipt_builtin_mt));
	xt_unregister_targets(ipt_builtin_tg, ARRAY_SIZE(ipt_builtin_tg));
	unregister_pernet_subsys(&ip_tables_net_ops);
}
