kernel: use-after-free due to race condition in qdisc_graft()

A use-after-free flaw was found in qdiscgraft in net/sched/schapi.c in the Linux Kernel due to a race problem. This flaw leads to a denial of service issue. If patch ebda44da44f6 "net: sched: fix race condition in qdiscgraft" not applied yet, then kernel could be affected...