KBS: add more context for Protocol Version Mismatch

Signed-off-by: Xynnn007 <xynnn@linux.alibaba.com>

kbs/src/attestation/backend.rs

@@ -181,7 +181,7 @@ impl AttestationService {
         let version = Version::parse(&request.version).context("failed to parse KBS version")?;
         if !VERSION_REQ.matches(&version) {
             bail!(
-                "expected version: {}, requested version: {}",
+                "KBS Client Protocol Version Mismatch: expect {} while the request is {}",
                 *VERSION_REQ,
                 request.version
             );