submodule: bump openthread from `3ebc3d3` to `ff3cc7e`

[dependabot[bot]]

Bumps openthread from 3ebc3d3 to ff3cc7e.

Commits

• ff3cc7e [posix] remove use of core-internal types in netif.cpp platform (#9928)
• 4c34a0e [test] enhance test_netdata_publisher robustness (#9932)
• 542be0f [thread-cert] use ROUTER_STARTUP_DELAY in test_detach (#9933)
• e379f7c [mle] disable MLE retransmissions when detaching (#9929)
• See full diff in compare view

You can trigger a rebase of this PR by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot show ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)