Conntrack events for 2.6.x

I've separated out Patrick McHardy's conntrack events from the nfnetlink-ctnetlink patch and ported it to 2.6.x. The patch was posted to netfilter-devel, in case you're interested.

For those of you who don't know what this means: It means that the first part of what is required for a 2.6.x ct_sync port is now done ;)