submodule: bump openthread from `b5b5994` to `f81eebe` (#8)
submodule: bump openthread from `b5b5994` to `f81eebe` (#8)

Bumps [openthread](https://github.com/openthread/openthread) from `b5b5994` to `f81eebe`.
- [Commits](https://github.com/openthread/openthread/compare/b5b5994651d324fc283b43344c83691406798110...f81eebeb48fe72d0bfe3427a8cba0a17ef3f77d0)

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

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-samr21,openthread/ot-samr21