Load table action from json without 'name' field for BMV2

[VolodymyrPeschanenkoIntel]

This small changes in script allow to load table action from JSON file without name field.
Without this changes this example finished with the message:
Exception 'name'

[jafingerhut]

Given the documentation for the name and target keys of a table definition in the BMv2 JSON file that you can find here https://github.com/p4lang/behavioral-model/blob/main/docs/JSON_format.md, then search for the only occurrence of "name: this attribute", this change appears like a correct one to me, in order to handle a larger set of correct BMv2 JSON files. Pinging @antoninbas to see if he has any comment on this change, but I will approve this change regardless, in case he is busy.

[jafingerhut]

Looks good to me. It is a bit odd to have a test case that intentionally uses fields of a header that is known to be invalid, but I suspect it might be difficult to find another test case that triggers the same issue, and the compiler does give good warnings for the source program.

[antoninbas]

I didn't look at the test programs, and I would expect p4c to always generate the "name" attribute, but I agree with the change to bmv2stf.py. The "name" attribute is indeed optional.