RDMA/hns: Only assign dest_qp if IB_QP_DEST_QPN bit is set

Only when the IB_QP_DEST_QPN flag of attr_mask is set is it valid to
assign the dest_qp_num into the dest_qp field of qp context.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Shaobo Xu <xushaobo2@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>