tty: Don't forget to setup peers mode on restore

In commit c6bc7259c we've started to carry @mode of the
files we're opening on restore, implying they are
static and should not be changed. This is true for
regular files but the pty peers are created
dynamically so if someone have set some special
mode beore the checkpoint procedure we will fail
on restore when regular file engine test it. So lets
setup @mode unconditionally.

https://travis-ci.org/xemul/criu/jobs/140011141



Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>