submodule: bump openthread from f68eda9 to 43cb7a0

Bumps [openthread](https://github.com/openthread/openthread) from `f68eda9` to `43cb7a0`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@f68eda9...43cb7a0)

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

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