bnxt_en: Use existing MSIX vectors for all mqprio TX rings

We can now fully support sharing the same MSIX for all mqprio TX rings
belonging to the same ethtool channel with the new infrastructure:

1. Allocate the proper entries for cp_ring_arr in struct bnxt_cp_ring_info
to support the additional TX rings.

2. Populate the tx_ring array in struct bnxt_napi for all TX rings
sharing the same NAPI.

3. bnxt_num_tx_to_cp() returns the proper NQ/completion rings to support
the TX rings in the input.

4. Adjust bnxt_get_num_ring_stats() for the reduced number of ring
counters with the new scheme.

Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>