submodule: bump openthread from 854e92a to b0984af

Bumps [openthread](https://github.com/openthread/openthread) from `854e92a` to `b0984af`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@854e92a...b0984af)

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

Signed-off-by: dependabot[bot] <[email protected]>