submodule: bump openthread from fe7d34f to 4f2eec9

Bumps [openthread](https://github.com/openthread/openthread) from `fe7d34f` to `4f2eec9`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@fe7d34f...4f2eec9)

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

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