pkt_sched: Add some basic qdisc class ops verification. Was: [PATCH] sfq: add dummy bind/unbind handles

Verify in register_qdisc() some basic qdisc class handlers are present.
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>