submodule: bump third_party/openthread/repo from `71e6543` to `d346481` (#870)
submodule: bump third_party/openthread/repo from `71e6543` to `d346481` (#870)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `71e6543` to `d346481`.
- [Commits](https://github.com/openthread/openthread/compare/71e6543d9b207a8d06509ffeef6c276fb3f5dc2f...d3464814948a457f33b2df3a02856ab2f3533a19)

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

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