Loopback is incomplete

[mcches]

The following scenarios exist for client -> server within the same host:

(Only Tcp is shown, but we need to handle it for Udp as well)

// bind | connect

// 0s | 127.0.0.1
// client: local Ok(127.0.0.1:49582), peer Ok(127.0.0.1:1234)
// server: 127.0.0.1:49582, local Ok(127.0.0.1:1234), peer Ok(127.0.0.1:49582)

// 127.0.0.1 | 127.0.0.1
// client: local Ok(127.0.0.1:49622), peer Ok(127.0.0.1:1234)
// server: 127.0.0.1:49622, local Ok(127.0.0.1:1234), peer Ok(127.0.0.1:49622)

// 0s | 192.168.1.42
// client: local Ok(192.168.1.42:49716), peer Ok(192.168.1.42:1234)
// server: 192.168.1.42:49716, local Ok(192.168.1.42:1234), peer Ok(192.168.1.42:49716)

// 127.0.0.1 | 192.168.1.42
// Error: Os { code: 61, kind: ConnectionRefused, message: "Connection refused" }

The first two work as expected, including setting the correct local|peer_addr on each side of the stream. The last two cause panics today due to holes in the stop-gap implementation for loopback.

We need to address this with workarounds and/or include this in the refactor being discussed in #132 .