[NETFILTER]: Fix incorrect argument to ip_nat_initialized() in ctnetlink

ip_nat_initialized() takes enum ip_nat_manip_type as it's second argument,
not a hook number.

Noticed and initial patch by Marcus Sundberg <marcus@ingate.com>.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>