IB/hfi1: Add received request info to qp_stats

The rvt_ack_entry pointed to by s_tail_ack_queue provides important
info about the request that has just been processed or is being processed
on the responder side of a RC connection. This patch adds this info to
the qp_stats to assist debugging.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>