submodule: bump openthread from `bacf8d6` to `615e951` (#405)
submodule: bump openthread from `bacf8d6` to `615e951` (#405)

Bumps [openthread](https://github.com/openthread/openthread) from `bacf8d6` to `615e951`.
- [Commits](https://github.com/openthread/openthread/compare/bacf8d625f50dd5c4b415caee754c934ba1a262c...615e951ca9b378331bcf6a29151ed1c1cdf98ac1)

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

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

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-efr32,openthread/ot-efr32,openthread/ot-efr32