4618ee1496
netstack.ListenTCP requires a full host:port address; callers passing
the standard net.Listen form (":0" for any-interface ephemeral port)
would get ParseAddrPort error. Prepend "0.0.0.0" when the address
starts with ":" so the API matches Go's net.Listen behaviour.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>