RDMA/hns: Fix a missing validation check for sl

driver inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8HYV0



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After the user sets the sl value, the driver does not verify
the sl value, which may result in the user's configuration
value exceeding the system configuration specifications. This
patch adds validation for the validity of the user-configured
sl value.

Fixes: 11ef2ec6 ("RDMA/hns: Support DSCP of userspace")
Signed-off-by: Luoyouming <luoyouming@huawei.com>