submodule: bump openthread from `23bbde5` to `f81c0b5` (#25)
submodule: bump openthread from `23bbde5` to `f81c0b5` (#25)

Bumps [openthread](https://github.com/openthread/openthread) from `23bbde5` to `f81c0b5`.
- [Commits](https://github.com/openthread/openthread/compare/23bbde5c96cba146351349c692c8ad3337bf7fac...f81c0b50f0a3d6f51fb09162bf2511fc62f6e6fe)

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

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-cc2538,openthread/ot-cc2538