IB/hns: add self loopback for CM

This patch mainly adds self loopback support for CM.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Peter Chen <luck.chen@huawei.com>
Reviewed-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>