Should PNA support resubmit operation? Also: document details of recirculate operation behavior

[jafingerhut]

Radostin asked the question about resubmit operation during 2022-Oct-17 PNA meeting.

Andy's best guess: PNA will support clone and recirculate operations, and some targets may support a "loopback" operation to change the direction of a packet. However, resubmit seems of low utility, given that recirculate exists and lets the developer modify the packet, and user-defined metadata, and preserve both kinds of changes for the next pass of processing.

If we want recirculate to preserve all user-defined metadata that was modified during the pass through parser + mainControl + mainDeparser where the recirculate operation was invoked, we should ensure that this is documented explicitly in the specification.