Expose a `bind` method on `UnixStream`

[little-dude]

Is your feature request related to a problem? Please describe.

Although very unconventional, it may be useful to bind a unix socket to a specific path. In my case, the listener calls UnixStream::peer_addr() upon accepting an incoming connection, and the path contains information necessary to process the connection.

Describe the solution you'd like

Allow users to create a UnixStream bound to a specific path. socket2 exposes a bind for this. I'm not sure how to make this fully backward compatible in tokio case though, since UnixStream::connect is currently the only way to create a socket.

Describe alternatives you've considered

• creating a socket2 socket, using AsyncFd for the connection, then convert the socket into a tokio socket
• creating a socket2 socket, make a blocking connect call, then convert the socket into a tokio socket

[Darksonn]

This is unlikely to be exposed as a bind call on UnixStream. Rather, it makes more sense to provide a UnixSocket type analogous to TcpSocket.

[evanrittenhouse]

I'm interested in this, but don't have a ton of experience working with Unix sockets - I wonder if it makes sense to create a Socket trait and pull some of the methods out?