Add Module.requires_grad_ (#22576)
Summary:
addresses https://github.com/pytorch/pytorch/issues/20241
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22576
Differential Revision: D16149314
Pulled By: zou3519
fbshipit-source-id: 1cc4c1ec084df30e00e9ae73ce1a53494a034d5c
