submodule: bump openthread from 9e9522a to ae940e6 (#936)

Bumps [openthread](https://github.com/openthread/openthread) from `9e9522a` to `ae940e6`.
- [Commits](openthread/openthread@9e9522a...ae940e6)

---
updated-dependencies:
- dependency-name: openthread
  dependency-version: ae940e6df81788a4fbb590d89b5f70d6341e2fa7
  dependency-type: direct:production
...

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