Change log level to warning for replay checksum errors

When a transaction is replayed after a disconnect, but returns a different result than expected the
client will receive this error:

ERROR 1927 (70100): Transaction checksum mismatch encountered when replaying transaction.

On the MaxScale side the corresponding message

Checksum mismatch, transaction replay failed. Closing connection.

is only written if log_info is enabled though, so when using default settings it will not occur in the Maxscale error log.

As an error is sent to the client it would probably make more sense to also have it logger on error, or at least warning, level on the Maxscale side.