mount: save remapped links on tmpfs (v2)

For that mnt namespaces should be dumped after files.

v2: rework enumeration of namespaces in dump_mnt_namespaces()
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>