[Cake] flow isolation for ISPs

[Andy Furniss]

Jonathan Morton wrote:
> Also, Cake’s general philosophy of simplifying configuration means that it’s unlikely to ever support “lists” or “tables” of explicit parameters.  This is a conscious design decision to enable its use by relative non-experts.  Arguably, even some of the existing options could reasonably be streamlined away.

Maybe something as simple as hash on nf-mark?