Change the TX ring logic so that the index increments unbounded and
mask it only when needed.

Modify the existing macros so that the index is not masked.  Add a
new macro RING_TX() to mask it only when needed to get the index of
txr->tx_buf_ring[].
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20231120234405.194542-11-michael.chan@broadcom.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>