IB/rdmavt: Correct issues with read-mostly and send size cache lines

The s_ahgpsn was incorrectly placed in the read-mostly section of the QP
and the s_curr_size and s_hdrwords are oversized. The misplaced
s_ahgpsn will cause the read-mostly cachelines to thrash.

Place s_ahgpsn in the send side cache lines and correctly size and
s_hdrwords and s_cur_size to keep the send side cachelines at the same
size.

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>