This reverts commit f92b40a8
("netfilter: core: only allow one nat hook per hook point"), this
limitation is no longer needed.  The nat core now invokes these
functions and makes sure that hook evaluation stops after a mapping is
created and a null binding is created otherwise.
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>