Reopen PR for 0 dim batch size for AvgPool2d. (#47426)
Summary:
Resubmitting https://github.com/pytorch/pytorch/pull/40694 since it could not be landed for some reason.
CC ngimel
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47426
Reviewed By: mruberry
Differential Revision: D24941350
Pulled By: ngimel
fbshipit-source-id: b7e50346d86eb63aaaf4fdd5ee71fafee2d0b476
