Changes for language spec update? compiler-inserted default_action is not const

[jafingerhut]

This issue is related to the following change made from v1.2.3 to v1.2.4 of the P4_16 language specification:

• compiler-inserted default_action is not const (Section 14.2).

Basically, if a table definition has no explicit default_action property, the compiler behaves as if the user wrote the property default_action = NoAction();, and adds NoAction to the list of actions if it was not there already.

(see https://p4.org/p4-spec/docs/P4-16-v1.2.4.html#sec-summary-of-changes-made-in-version-124 for the item in context of the full list of changes, but there are separate Github issues for each that might impact the P4Runtime API specification).

This seems worth at least briefly discussing in API work group, but my guess is that this is really just a clarification in the language spec that says explicitly what has already been done for years in the open source P4 implementations.

[jafingerhut]

2023-Sep-08: Decision made that no P4Runtime spec changes needed, so remove this item from bullet list in spec.

[jafingerhut]

This issue can be closed if/when PR #459 is merged.

[jafingerhut]

PR #459 was merged, so closing this issue as resolved.