[NETFILTER]: netns: put table module on netns stop

When number of entries exceeds number of initial entries, foo-tables code
will pin table module. But during table unregister on netns stop,
that additional pin was forgotten.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>