RDMA/hns: Reduce PFC in congestion scene

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

The original one is to send 16 packets at one time, and now it is
configured to send 1 packet once. This parameter is tested to make
sure performance reach the standard.

Feature or Bugfix: Bugfix

Signed-off-by: Sirong Wang <wangsirong@huawei.com>
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Reviewed-by: chenglang <chenglang@huawei.com>
Reviewed-by: liuyixian <liuyixian@huawei.com>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>