[WIP] SOC_U: Implemented some socket functions

This allows ftpony and ftbrony to work.
It's using Berkeley sockets directly since that's what the soc:U service exposes to applications.

Still WIP.
Can't you create a dummy handle in the handle table instead? I'm worried that programs will try to use 0 (not a valid handle) as a sigil value internally which will fail with this.