submodule: bump openthread from da72435 to 0c6c2fe (#710)

Bumps [openthread](https://github.com/openthread/openthread) from `da72435` to `0c6c2fe`.
- [Commits](openthread/openthread@da72435...0c6c2fe)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>