`clientError` will have `http.Server`-specific behavior, and we don't
want to shadow it in `tls.Server`.

Make default `clientError` behavior (close socket immediately)
overridable. With this APIs it is possible to write a custom error
handler, and to send, for example, a 400 HTTP response.

    http.createServer(...).on('clientError', function(err, socket) {
      socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
      socket.destroy();
    });

Fix: nodejs#4543