netfilter: arptables: use pernet ops struct during unregister

Like with iptables and ebtables, hook unregistration has to use the
pernet ops struct, not the template.

This triggered following splat:
  hook not found, pf 3 num 0
  WARNING: CPU: 0 PID: 224 at net/netfilter/core.c:480 __nf_unregister_net_hook+0x1eb/0x610 net/netfilter/core.c:480
[..]
 nf_unregister_net_hook net/netfilter/core.c:502 [inline]
 nf_unregister_net_hooks+0x117/0x160 net/netfilter/core.c:576
 arpt_unregister_table_pre_exit+0x67/0x80 net/ipv4/netfilter/arp_tables.c:1565

Fixes: f9006acc ("netfilter: arp_tables: pass table pointer via nf_hook_ops")
Reported-by: syzbot+dcccba8a1e41a38cb9df@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter_arp/arp_tables.h

@@ -53,8 +53,7 @@ int arpt_register_table(struct net *net, const struct xt_table *table,
 			const struct arpt_replace *repl,
 			const struct nf_hook_ops *ops);
 void arpt_unregister_table(struct net *net, const char *name);
-void arpt_unregister_table_pre_exit(struct net *net, const char *name,
-				    const struct nf_hook_ops *ops);
+void arpt_unregister_table_pre_exit(struct net *net, const char *name);
 extern unsigned int arpt_do_table(struct sk_buff *skb,
 				  const struct nf_hook_state *state,
 				  struct xt_table *table);

net/ipv4/netfilter/arp_tables.c

@@ -1556,13 +1556,12 @@ int arpt_register_table(struct net *net,
 	return ret;
 }
 
-void arpt_unregister_table_pre_exit(struct net *net, const char *name,
-				    const struct nf_hook_ops *ops)
+void arpt_unregister_table_pre_exit(struct net *net, const char *name)
 {
 	struct xt_table *table = xt_find_table(net, NFPROTO_ARP, name);
 
 	if (table)
-		nf_unregister_net_hooks(net, ops, hweight32(table->valid_hooks));
+		nf_unregister_net_hooks(net, table->ops, hweight32(table->valid_hooks));
 }
 EXPORT_SYMBOL(arpt_unregister_table_pre_exit);
 

net/ipv4/netfilter/arptable_filter.c

@@ -54,7 +54,7 @@ static int __net_init arptable_filter_table_init(struct net *net)
 
 static void __net_exit arptable_filter_net_pre_exit(struct net *net)
 {
-	arpt_unregister_table_pre_exit(net, "filter", arpfilter_ops);
+	arpt_unregister_table_pre_exit(net, "filter");
 }
 
 static void __net_exit arptable_filter_net_exit(struct net *net)