iproute2: cake: support new operating modes

iproute2: cake: support new operating modes

There has been recent significant activity with the cake qdisc of late
Some of that effort is related to upstreaming to kernel & iproute2
mainline but we're not quite there yet.  This commit teaches tc how to
activate and interprete the latest cake operating modes, namely:

ingress mode: Instead of only counting packets that make it past the
shaper, include packets we've decided to drop as well, since they did
arrive with us on the link and took link capacity.
This mode is more suitable for shaping the ingress of a link
(e.g. from ISP) rather than the more normal egress.

ack-filter/ack-filter-aggressive: Filter excessive TCP ACKS.  Useful in
highly assymetric links (downstream v upstream capacity) where the
majority of upstream link capacity is occupied with ACKS for downstream
traffic.

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