vdso: Defer handling untill all zones are restored

In worst case we might be tryin to proxify vdso zone
when vvar only is remmaped but vdso itself is not yet
(left and right zones shifting). Thus vdso_proxify
will complain that vdso is not yet mapped refusing
to restore.

Thus wait until everything is re-mapped then call
for proxification helper.

Reported: Mr. Jenkins
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>