Resolving the template in userspace (LinkList then TUNSETIFF) races with
concurrent instances: both can pick nebula0, and with multiqueue the loser
silently attaches as a second queue to the winner's device instead of
failing. TUNSETIFF natively substitutes a single %d via dev_alloc_name,
atomically and always allocating a fresh device, so keep the fail-fast
validation but pass the template through and read the resolved name back.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Fg7oD3uZ4jZjjQ4gRsPAwB