CVE-2024-35892 net/sched: fix lockdep splat in qdisc_tree_reduce_backlog()

In the Linux kernel, the following vulnerability has been resolved: net/sched: fix lockdep splat in qdisctreereducebacklog qdisctreereducebacklog is called with the qdisc lock held, not RTNL. We must use qdisclookuprcu instead of qdisclookup syzbot reported: WARNING: suspicious RCU usage...