RDMA/hns: Reduce PFC frames in congestion scenarios

The original value means sending 16 packets at a time, and it should be
configured to 0 which means sending 1 packet instead. It is modified to
reduce the number of PFC frames to make sure the performance meets
expectations when flow control is enabled on hip08.

Link: https://lore.kernel.org/r/1585194018-4381-2-git-send-email-liweihang@huawei.com


Signed-off-by: Jihua Tao <taojihua4@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>