update gloo submodule (#101472)

Ran command: `git submodule update --remote -- third_party/gloo`

This is to pull in changes up to facebookincubator/gloo@31b1f02 to enhance gloo scalability for large distributed training jobs running into ephemeral port exhaustion issues.

The test failure in #101438 shows the need for that.

Pull Request resolved: #101472
Approved by: https://github.com/H-Huang