log message for InvalidMagicNumberException may be incorrect

For security mode, HDFS now supports that Datanodes don't require root or jsvc if dfs.data.transfer.protection is configured.

Log message for InvalidMagicNumberException, we miss one case:
when the datanodes run on unprivileged port and dfs.data.transfer.protection is configured to authentication but dfs.encrypt.data.transfer is not configured. SASL handshake is required and a low version dfs client is used, then InvalidMagicNumberException is thrown and we write log:

Failed to read expected encryption handshake from client at .... Perhaps the client is running an older version of Hadoop which does not support encryption

Recently I run HDFS built on trunk and security is enabled, but the client is 2.5.1 version. Then I got the above log message, but actually I have not configured encryption.