Fix QConfig_dynamic typename (#24431)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24431
Pickle's fully-qualified name lookup would fail when trying to serialize QConfig_dynamic since the __name__ on the instance would refer to the wrong class name
Test Plan: Imported from OSS
Differential Revision: D16835705
Pulled By: jamesr66a
fbshipit-source-id: e146835cbe10b08923d77298bc93b0f5b0ba37c5
