sch_htb: let skb->priority refer to non-leaf class

If the class in skb->priority is not a leaf, apply filters from the
selected class, not the qdisc. This lets netfilter or user space
partially classify the packet.

Signed-off-by: Harry Mason <harry.mason@smoothwall.net>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>