Revert "netfilter: x_tables: Update remaining dereference to RCU"

This reverts commit 443d6e86.

This (and the following) patch basically re-implemented the RCU
mechanisms of patch 78454473. That patch was replaced because of the
performance problems that it created when replacing tables. Now, we have
the same issue: the call to synchronize_rcu() makes replacing tables
slower by as much as an order of magnitude.

Revert these patches and fix the issue in a different way.
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/arp_tables.c

@@ -1379,7 +1379,7 @@ static int compat_get_entries(struct net *net,
 	xt_compat_lock(NFPROTO_ARP);
 	t = xt_find_table_lock(net, NFPROTO_ARP, get.name);
 	if (!IS_ERR(t)) {
-		const struct xt_table_info *private = xt_table_get_private_protected(t);
+		const struct xt_table_info *private = t->private;
 		struct xt_table_info info;
 
 		ret = compat_table_info(private, &info);

net/ipv4/netfilter/ip_tables.c

@@ -1589,7 +1589,7 @@ compat_get_entries(struct net *net, struct compat_ipt_get_entries __user *uptr,
 	xt_compat_lock(AF_INET);
 	t = xt_find_table_lock(net, AF_INET, get.name);
 	if (!IS_ERR(t)) {
-		const struct xt_table_info *private = xt_table_get_private_protected(t);
+		const struct xt_table_info *private = t->private;
 		struct xt_table_info info;
 		ret = compat_table_info(private, &info);
 		if (!ret && get.size == info.size)

net/ipv6/netfilter/ip6_tables.c

@@ -1598,7 +1598,7 @@ compat_get_entries(struct net *net, struct compat_ip6t_get_entries __user *uptr,
 	xt_compat_lock(AF_INET6);
 	t = xt_find_table_lock(net, AF_INET6, get.name);
 	if (!IS_ERR(t)) {
-		const struct xt_table_info *private = xt_table_get_private_protected(t);
+		const struct xt_table_info *private = t->private;
 		struct xt_table_info info;
 		ret = compat_table_info(private, &info);
 		if (!ret && get.size == info.size)