IB/hfi1: Move rhf_offset from devdata to ctxtdata

This field should be in ctxtdata to allow for better locality of access by
eliminating a dd dereference.

The new field is now side-by-side with rcvhdrqentsize since the rhf_offset
is a function of the rcvhdrqentsize.

Both fields are now correctly sized as u8.

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>