(EncoderDecoderModel) Why decoder_start_token_id are different between train and generation?
As source code given below from [EncoderDecoderModel](https://huggingface.co/transformers/model_doc/encoderdecoder.html?highlight=decoder_start_token#transformers.EncoderDecoderModel.forward), **decoder_start_token_id** are different between train and generation.

```
>>> # training
>>> model.config.decoder_start_token_id = tokenizer.cls_token_id
```

```
>>> # generation
>>> generated = model.generate(input_ids, decoder_start_token_id=model.config.decoder.pad_token_id)
```

Why they are not same?