Function connect_transport_site_with_loopback 

pub fn connect_transport_site_with_loopback(
    cx: &mut Cx,
    address: ServerAddress,
    offered_codecs: Vec<Symbol>,
    allow_loopback: bool,
) -> Result<(Arc<dyn EvalSite>, Symbol)>

Connects to address, returning the eval site plus negotiated codec.

When allow_loopback is set, a connection that fails may fall back to a registered in-process endpoint for the same address.