net/bnxt: update external action record pool

net/bnxt: update external action record pool

- Added support variable sized action records
- Additional error checking on table scope params
- Single external pool supported per direction
- Changed to return action record pointer
- Allows action pool to fully utilize the number of flows

Signed-off-by: Farah Smith <farah.smith@broadcom.com>
Signed-off-by: Mike Baucom <michael.baucom@broadcom.com>
Reviewed-by: Peter Spreadborough <peter.spreadborough@broadcom.com>
Reviewed-by: Kishore Padmanabha <kishore.padmanabha@broadcom.com>