Improve readability of sai_api_gen.py for SAI header file generation. (…

…sonic-net#470)

* temp checkin.

* temp checkin.

* Update SAI to reference.

* table data parser.

* DASH API set object.

* minor update.

* Table keys and types.

* table action and param.

* fix v4_or_v6 fields.

* Simplify template based file generation code.

* Revert to current SAI

* SAI Generator.

* Fix header generation issues.

* Fix lib generation issue.

* Fix ignored tables.