Only reason for having two different register functions was because of
ipt_MASQUERADE and ip6t_MASQUERADE being two different modules.

Previous patch merged those into xt_MASQUERADE, so we can merge this too.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>