RDMA/hns: Add check for the validity of sl configuration

According to the RoCE v1 specification, the sl (service level) 0-7 are
mapped directly to priorities 0-7 respectively, sl 8-15 are reserved. The
driver should verify whether the the value of sl is larger than 7, if so,
an exception should be returned.

Fixes: 926a01dc

 ("RDMA/hns: Add QP operations support for hip08 SoC")
Link: https://lore.kernel.org/r/1600509802-44382-5-git-send-email-liweihang@huawei.com
Signed-off-by: Jiaran Zhang <zhangjiaran@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>