init: increment stat count if parent == default thread

We skip doing the stat increment if group_reporting is set,
but that means we can end up with stat_number == 0. That
isn't correct, increment for group_reporting as well, but
only if the parent is the default thread. That means we
still won't do it for sub-jobs.

Signed-off-by: Jens Axboe <axboe@fb.com>