"Whoop whoop, sound of da police"

Add an ingress capable traffic policer module configurable with tc.

From the man page:

The police action allows to limit bandwidth of traffic matched by the
filter it is attached to. Basically there are two different algorithms
available to measure the packet rate: The first one uses an internal
dual token bucket and is configured using the rate, burst, mtu,
peakrate, overhead and linklayer parameters. The second one uses an
in-kernel sampling mechanism. It can be fine-tuned using the estimator
filter parameter.

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