static void decrement_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
{
	b->p_mark = prob_minus(b->p_mark, q->decrement);
}
static void decrement_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
{
	b->p_mark = prob_minus(b->p_mark, q->decrement);
}