Modules pre-load is also slow, but guarding this code with
the presence of criu.kdat cache file seems reasonable.

Or course, one may unload the needed modules by hands, but
such smart user may as well remove the /run/criu.kdat file :)
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>