RDMA/hns: Optimize hns_roce_modify_qp function

Here mainly packages some code into some new functions in order to
reduce code compelexity.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Link: https://lore.kernel.org/r/1565276034-97329-3-git-send-email-oulijun@huawei.com


Signed-off-by: Doug Ledford <dledford@redhat.com>