prevent overriding shuffle settings in DataLoader for datapipes
Fixes https://github.com/pytorch/data/issues/295
Follow-up to https://github.com/pytorch/pytorch/pull/75014#issuecomment-1091921305. We only need to update locations where we actually check `shuffle` for identity with a boolean value, i.e. `shuffle is False`. For bool-ish checks like `if shuffle:`, `None` behaves just like `False`.
`IterDataPipe`'s are currently not mentioned in the docstring. Since this change only applies to them, I didn't update it. LMK, if I should do that.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75505
Approved by: https://github.com/ejguan
