IB/hfi1: Fix yield logic in send engine

When there are many RC QPs and an RDMA READ request
is sent, timeouts occur on the requester side because
of fairness among RC QPs on their relative SDMA engine
on the responder side.  This also hits write and send, but
to a lesser extent.

Complicating the issue is that the current code checks if workqueue
is congested before scheduling other QPs, however, this
check is based on the number of active entries in the
workqueue, which was found to be too big to for
workqueue_congested() to be effective.

Fix by reducing the number of active entries as revealed by
experimentation from the default of num_sdma to
HFI1_MAX_ACTIVE_WORKQUEUE_ENTRIES.  Retry counts were monitored
to determine the correct value.

Tracing to investigate any future issues is also added.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Sebastian Sanchez <sebastian.sanchez@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>