Added relu6 kernel (#24799)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24799
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24799
Differential Revision: D16875493
Test Plan: Imported from OSS
Pulled By: zafartahirov
fbshipit-source-id: 0d256db193c6a8e0d37dbdf6cf35dd031fd4ec6c
