submodule: bump openthread from d0f6d17 to f68eda9

Bumps [openthread](https://github.com/openthread/openthread) from `d0f6d17` to `f68eda9`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@d0f6d17...f68eda9)

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

Signed-off-by: dependabot[bot] <support@github.com>