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

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

This reverts commit 78f1ea0b998db105e12a4abd2eeb32bd0bac98de.

This (and the following) patch basically re-implemented the RCU
mechanisms of patch 8abf527013d4. 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>