IB/hfi1: Remove rcvhdrq_size

The usage of this ctxt data field is not hot path and the value can be
computed on demand to cut down the ctxtdata bloat.

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>