sch_netem: Replace ->requeue() method with open code

After removing netem classful functionality we are sure its inner
qdisc is tfifo, so we can replace qdisc->ops->requeue() method with
open code. After this patch there are no more ops->requeue() users.

The idea of this patch is by Patrick McHardy.

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>