submodule: bump openthread from d81c6fa to f40eeeb

Bumps [openthread](https://github.com/openthread/openthread) from `d81c6fa` to `f40eeeb`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@d81c6fa...f40eeeb)

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

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