Update nccl submodule to v2.4.6 (#20882)
Summary:
Fixes #20630
Haven't tested it yet. Let's see if it passes all CI tests.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20882
Reviewed By: pietern
Differential Revision: D15483561
Pulled By: mrshenli
fbshipit-source-id: 5f0730a04d92906af077b2fe2170b674ca371e6c
