IB/rdmavt: Max atomic value should be a u8

This matches the ib_qp_attr size and
avoids a extremely large value when the lower level
driver registers.

As part of the patch, the u8 ordinals are moved to the
end of the struct to reduce pahole noted excesses.

Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>