v2: Fixed the very obvious lack of setting ucounts
    on struct mnt_ns reported by Andrei Vagin, and the kbuild
    test report.
Reported-by: Andrei Vagin <avagin@openvz.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>