[PATCH 2.4] Use double-linked list for dev->qdisc_list

This patch changes dev->qdisc_list to a double-linked list. This solves
the performance problems when destroying qdiscs with large number of inner
qdiscs.

This is backported version of Patrick McHardy patch (03-qdisc_list-list_h.diff)
for 2.6 kernels.

-- 
Tomasz Paszkowski