submodule: bump openthread from da72435 to 0c6c2fe

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

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

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