ctnetlink updates

Hi Patrick,

The following patchset includes several updates for ctnetlink. Its purpose is to resolve the remaining issues so that we can unlabel it as experimental in the near future. I'd like to release the first 1.0 of the conntrack-tools by the end of the year and it would be great if we can have this marked as a stable feature before doing so.

AFAIK, another remaining issues are the removal of the notifier call chain and the NAT dependency. Could you point out the preferred way to do this?

Thanks.

"Los honestos son inadaptados sociales" -- Les Luthiers