fixes multiprocessing serialization for integer nn.Parameter (#18639)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/17345
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18639
Differential Revision: D14711565
Pulled By: soumith
fbshipit-source-id: 0063ed138a215b95d6571dcd68b18569714abe19
