Ensure that DDP wrapped module has parameters that require gradients (#25858)
Summary:
…ent - see https://github.com/pytorch/pytorch/issues/25552
**TEST PLAN**
```
python test/run_test.py -f distributed
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25858
Differential Revision: D17687542
Pulled By: danthe3rd
fbshipit-source-id: 11bfe4142e72bb21382b30379fe10e60418c7ec9
