BatchNorm autodiff re-enabled (#57321)
Summary:
Turns on BN in autodiff:
1. outputs an empty tensor for running stats to by pass autodiff issue on None;
2. fixing BN inference backward in cudnn & miopen, where backward falls back to native batchnorm kernel instead;
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57321
Reviewed By: albanD, ngimel
Differential Revision: D30250419
Pulled By: jansel
fbshipit-source-id: a62553789c20fb50a820003a056f40d9d642dfaa
