user namespace: make each net (net_ns) belong to a user_ns

This way we can target capabilites at the user_ns which created the
net ns.

Changelog:
   jul 8: nsproxy: don't assign netns->userns if not cloning.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
3 files changed