RDMA/hns: Reduce the maximum number of extend SGE per WQE

Just reduce the default number to 64 for backward compatibility, the
driver can still get this configuration from the firmware.

Link: https://lore.kernel.org/r/1585194018-4381-3-git-send-email-liweihang@huawei.com


Signed-off-by: Lang Cheng <chenglang@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>