submodule: bump openthread from `dbf475f` to `b6cc940` (#274)
submodule: bump openthread from `dbf475f` to `b6cc940` (#274)

Bumps [openthread](https://github.com/openthread/openthread) from `dbf475f` to `b6cc940`.
- [Commits](https://github.com/openthread/openthread/compare/dbf475f066630ea582d261d24ff0c223ae6a92f3...b6cc940634d2c0af4c953d85b524bafbb72abefe)

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

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-nrf528xx,openthread/ot-nrf528xx