Merge branch 'net_sched-no-longer-use-qdisc_tree_flush_backlog'

Eric Dumazet says:

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net_sched: no longer use qdisc_tree_flush_backlog()

This series is based on a report from Gerrard Tai.

Essentially, all users of qdisc_tree_flush_backlog() are racy.

We must instead use qdisc_purge_queue().
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Link: https://patch.msgid.link/20250611111515.1983366-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>