Fixed buffer update in BatchNorm when track_running_stats is set to False (#38084)
Summary:
This PR aims at tackling https://github.com/pytorch/pytorch/issues/37823 by:
- ensuring that buffers will be used for normalization computation but won't be updated, when buffers are not None, and `track_running_stats=False`
- adding a corresponding unittest to ensure expected behaviour
Any feedback is welcome!
_Note: we might want to update the docstrings of `BatchNorm*d`, feel free to share any suggestion!_
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38084
Differential Revision: D22047871
Pulled By: ezyang
fbshipit-source-id: 5acbcad9773e7901f26d625db71d43d7dc236d3e
