RFC: net/netfilter reorganization

[Patrick McHardy <kaber@trash.net>]

We've talked about reorganizing net/netfilter in a smaller group
during the workshop. Its currently quite crowded in there,
additionally the IPVS guys are moving their code under
net/netfilter/ipvs in 2.6.28.

Some suggestions for a new directory structure:

net/netfilter/xtables
net/netfilter/{ct, conntrack, nfct, ...}
net/netfilter/nftables for my new stuff

We could go further by splitting up xtables and conntrack,
parts of this structure would be mirrored in net/ipv4/netfilter
and net/ipv6/netfilter:

net/netfilter/xtables/matches
net/netfilter/xtables/targets
net/netfilter/ct/protocols
net/netfilter/ct/helpers

I'm not sure whether this is too much since 4 directory
levels seem a bit extreme.

Since the amount of core code is increasing too, one more
thought was

net/netfilter/core

containing core.c, netfilter.c, logging and queuing stuff and
everything netlink related that doesn't fall in a more specific
area.