It looks like a namespace for service descriptors.
It will be used for restoring tasks with shared fd tables.
Service descriptors should be own for each process.

v2: clone_service_fd doesn't know about sub-systems like log, proc, etc
v3: Don't try to find a free name-space.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>