netfilter: ipvs: prepare for hook function reduction

ipvs has multiple one-line wrappers for hooks, compact them.

To avoid a large patch make the two most common helpers use the same
function signature as hooks.

Next patches can then remove the oneline wrappers.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>