cake: bump to 20180504 bake

cake: bump to 20180504 bake

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Cake is bearing fruits of kernel upstreaming efforts.

diffserv-llt dropped. DSCP mapping paper died and no one using it.

ack-filter re-written & simplified

tc userspace & cake kmod netlink interface usage changed in non
backwards compatible way, thus this once requires tc & cake to be
in-step.  Change due to upstream requirements.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>