[qat]Make sure the bn statistics are the same in the unit test. (#66244)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66244
Make sure the bn statistics are the same in the unit test.
* The fused model in the existing code will have different bn statistics compared to the model without fusion. They will produce the same result when the model is in training mode, but different result in eval mode.
Test Plan: buck run mode/dev-nosan //caffe2/test:quantization -- -r quantization.eager.test_fusion.TestFusion
Reviewed By: jerryzh168
Differential Revision: D29504500
fbshipit-source-id: 41e3bfd7c652c27619baa7cbbe98d8d06a485781
