netfilter: x_tables: unregister the templates first

netfilter: x_tables: unregister the templates first

When the module is going away we need to zap the template
first.  Else there is a small race window where userspace
could instantiate a new table after the pernet exit function
has removed the current table.

Fixes: fdacd57c79b7 ("netfilter: x_tables: never register tables by default")
Reported-by: Tristan Madani <tristan@talencesecurity.com>
Reviewed-by: Tristan Madani <tristan@talencesecurity.com>
Closes: https://lore.kernel.org/netfilter-devel/20260429175613.1459342-1-tristmd@gmail.com/
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>