submodule: bump openthread from cc31b64 to c5108df (#1133)

Bumps [openthread](https://github.com/openthread/openthread) from `cc31b64` to `c5108df`.
- [Commits](openthread/openthread@cc31b64...c5108df)

---
updated-dependencies:
- dependency-name: openthread
  dependency-version: c5108df3e3a4537b7b54602fb6f8182c74306693
  dependency-type: direct:production
...

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