RDMA/hns: Configure ecn field of ip header

In order to compatible with the third party RoCE device, The hardware
modify the set method for the ecn field of ip header in new hip08
version. The high 6bit of tclass be assigned for dscp field of packet.

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