IB/hfi1: Rightsize ctxt_eager_bufs fields

Fields in this structure are sized excessively based on hardware
limitations and input values.

Fix by reducing fields as appropriate and repositioning to close holes in
the structure.

Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>