submodule: bump openthread from `6680233` to `864c4be` (#39)
submodule: bump openthread from `6680233` to `864c4be` (#39)

Bumps [openthread](https://github.com/openthread/openthread) from `6680233` to `864c4be`.
- [Commits](https://github.com/openthread/openthread/compare/66802336dec9b8ba4850b054615fe79bf8a01c4a...864c4be9e5e8643440f5a1d5a277db175aa45b49)

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

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