Rollup patch to add LXC support

This is as much for the purpose of getting this patch out somewhere as actually requesting that you pull it. This is *enough* to support LXC on a Nexus 9, but there's still problems which mean that I don't have it fully working yet--you can't mount more than one cgroup on the same mount point for some reason, which breaks the LXC Android wrapper script.

Anyways, in the off chance that you're interested, I built it on your kernel sources, so I figured I'd make a pull request.

Nearly every change is a result of older code which expects `int`s for UID or GID. However, with namespaces, you need to use `kgid_t` or `kuid_t` structures, respectively.