submodule: bump openthread from e5aaa57 to c545835 (#884)

Bumps [openthread](https://github.com/openthread/openthread) from `e5aaa57` to `c545835`.
- [Commits](openthread/openthread@e5aaa57...c545835)

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

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