submodule: bump openthread from fd2e06d to a2d65a1 (#880)

Bumps [openthread](https://github.com/openthread/openthread) from `fd2e06d` to `a2d65a1`.
- [Commits](openthread/openthread@fd2e06d...a2d65a1)

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

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