More netfilter work at workshop coding day 1

After having terminated the traditional workshop part, we've today had day 1 of the workshop.netfilter.org hacking sessions.

Despite the different topic, I spent the better part of the day with Michael Bellion and Henrik Nordstrom working out the details of nf-hipac / nfnetlink integration.

Apart from that, there's now a nf_conntrack header cleanup in my git tree, I've ported ebt_[u]log to nf[netlink]_log, fixed some minor Kconfig issues, merged some patches from Yasuyuki and Pablo, and pushed forward a round of fixes and updates to DaveM.