Zefan Li requested [1] to perform the following cleanup/refactoring:

- Split cgroupfs classid handling into net core to better express a
  possible more generic use.

- Disable module support for cgroupfs bits as the majority of other
  cgroupfs subsystems do not have that, and seems to be not wished
  from cgroup side. Zefan probably might want to follow-up for netprio
  later on.

- By this, code can be further reduced which previously took care of
  functionality built when compiled as module.

cgroupfs bits are being placed under net/core/netclassid_cgroup.c, so
that we are consistent with {netclassid,netprio}_cgroup naming that is
under net/core/ as suggested by Zefan.

No change in functionality, but only code refactoring that is being
done here.

 [1] http://patchwork.ozlabs.org/patch/304825/Suggested-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NDaniel Borkmann <dborkman@redhat.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: Thomas Graf <tgraf@suug.ch>
Cc: cgroups@vger.kernel.org
Acked-by: NLi Zefan <lizefan@huawei.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>