IB/ehca: Correctly set GRH mask bit in ehca_modify_qp()

The driver needs to always supply the "GRH present" flag to the
hypervisor, whether it's true or false. Not supplying it (i.e. not
setting the corresponding mask bit) amounts to a "perhaps", which we
don't want.

Signed-off-by: Joachim Fenkes <fenkes@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>