Base hparams for TransformerRevnet.

def transformer_revnet_base():
  """Base hparams for TransformerRevnet."""
  hparams = transformer.transformer_big()

  # Use settings from transformer_n_da
  hparams.layer_preprocess_sequence = "n"
  hparams.layer_postprocess_sequence = "da"
  hparams.learning_rate = 0.4

  return hparams