net_sched: fix skb memory leak in deferred qdisc drops

In the Linux kernel, the following vulnerability has been resolved:

net_sched: fix skb memory leak in deferred qdisc drops

When the network stack cleans up the deferred list via qdisc_run_end(),

it operates on the root qdisc. If the root qdisc do not implement the

TCQ_F_DEQUEUE_DROPS flag the packets queue to free are never freed and

gets stranded on the child's local to_free list.

Fix this by making qdisc_dequeue_drop() aware of the root qdisc. It

fetches the root qdisc and check for the TCQ_F_DEQUEUE_DROPS flag. If

the flag is present, the packet is appended directly to the root's

to_free list. Otherwise, drop it directly as it was done before the

optimization was implemented.