[Gradient Compression] Rename the first arg of pybinding of _register_comm_hook: ddp_model -> reducer. (#46498)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46498
The name of the first arg "ddp_model" is misleading, because it is actually the reducer of DDP model rather than entire model.
This method is called in the file caffe2/torch/nn/parallel/distributed.py:
`dist._register_comm_hook(self.reducer, state, hook)`
ghstack-source-id: 114531188
(Note: this ignores all push blocking failures!)
Test Plan: waitforbuildbot
Reviewed By: pritamdamania87
Differential Revision: D24372827
fbshipit-source-id: dacb5a59e87400d93a2f35da43560a591ebc5499
