RDMA/hns: Only assgin the fields of the av if IB_QP_AV bit is set

Only when the IB_QP_AV flag of attr_mask is set is it valid to assign the
related fields of the av into the qp context.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>