[Cake] [PATCH net] sch_cake: Take advantage of skb->hash where appropriate

[Toke Høiland-Jørgensen]

> The immediate motivation for fixing this was the recent patch to WireGuard
> to preserve the skb->hash on encapsulation. As such, this is also what I
> tested against; with this patch, added latency under load for competing
> flows drops from ~8 ms to sub-1ms on an RRUL test over a WireGuard tunnel
> going through a virtual link shaped to 1Gbps using sch_cake. This matches
> the results we saw with a similar setup using sch_fq_codel when testing the
> WireGuard patch.

See attached Flent data files for the full results (dropping netdev@ for
these).

-Toke

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