Docker requested an option, when network devices and routes are not
dumped and not restored. Instead of this Docker will call libnetwork
hook to tune netns from the setup-namespaces action.

Cc: Saied Kazemi <saied@google.com>
Tested-by: Ross Boucher <boucher@gmail.com>
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>