print_on_level(): simplify off setting code

This is a slight refactoring of commit 7de96526, which just simplifies
initialization of 'off' variable, and adds the comment why we do so.
Should make the next patch easier to read.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>