[DataPipe] Fixing pickling issues with fork and demux (#67930)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/67930
Fixes #67848
Test Plan: Imported from OSS
Reviewed By: H-Huang
Differential Revision: D32222184
Pulled By: NivekT
fbshipit-source-id: 48871c45a855d92cd599e21f3b53827dd32c91ef
