IB/hfi1: Tune netdev xmit cachelines

This patch moves fields in the ring and creates a line for the producer
and the consumer.

The adds a consumer side variable that tracks the ring avail so that the
code doesn't have the read the other cacheline to get a count for every
packet. A read now only occurs when the avail is at 0.

Fixes: d99dc602 ("IB/hfi1: Add functions to transmit datagram ipoib packets")
Link: https://lore.kernel.org/r/20210913132842.131370.15636.stgit@awfm-01.cornelisnetworks.com


Reviewed-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>