When transport_tcp feature is enabled, default listen endpoints are (as before) :

{
    router: ["tcp/[::]:7447"],
    peer: ["tcp/[::]:0"],
    client: [],
}

When transport_tcp feature is disabled, default listen endpoints are (now) :

{
    router: [],
    peer: [],
    client: [],
}

This avoids having this error: Unsupported protocol: tcp. when running a router or peer build with transport_tcp feature disabled and the default config.