caching or preprocessing layer for forwarding decisions

[niksu]

Since forwarding decisions are immutable, instead of allocating objects for forwarding decisions we could cache similar earlier decisions. This could take the form of a general caching layer, which users of Pax could tune or extend for their packet processors. Or it could take the form of a preprocessing step.

That is, instead of creating a new SinglePortForward each time we make a forwarding decision, if we have a single-port forwarding processor with 5 ports we could simply instantiate SinglePortForward 6 times (one for each port, and once for drop -- port -1) when the packet processor starts, then reference these instances during runtime.

Things might get a bit harder with MultiPortForward, where it might make more sense to have a caching layer rather than parameter-sweep at start-time as a preprocessing step.

For more context see #7 (comment)