submodule: bump third_party/openthread/repo from 700f624 to `6e7ed5…

…c` (#2098)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `700f624` to `6e7ed5c`.
- [Commits](openthread/openthread@700f624...6e7ed5c)

---
updated-dependencies:
- dependency-name: third_party/openthread/repo
  dependency-type: direct:production
...

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