pkt_sched: make qdisc_class_hash_alloc() static

This patch makes the needlessly global qdisc_class_hash_alloc() static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>