submodule: bump openthread from `543e32d` to `b4c76b3` (#196)
submodule: bump openthread from `543e32d` to `b4c76b3` (#196)

Bumps [openthread](https://github.com/openthread/openthread) from `543e32d` to `b4c76b3`.
- [Commits](https://github.com/openthread/openthread/compare/543e32d2aef7eda8d66396c93476ce0da4e13c5b...b4c76b3e170a729f9bdb57ddaa6d05b73e541ce2)

---
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