std: move network code into sys

As per rust-lang#117276, this PR moves `sys_common::net` and the `sys::pal::net` into the newly created `sys::net` module. In order to support rust-lang#135141, I've moved all the current network code into a separate `connection` module, future functions like `hostname` can live in separate modules.

I'll probably do a follow-up PR and clean up some of the actual code, this is mostly just a reorganization.

Author: joboet

std/src/net/socket_addr.rs

@@ -6,8 +6,7 @@ mod tests;
 pub use core::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
 
 use crate::net::{IpAddr, Ipv4Addr, Ipv6Addr};
-use crate::sys::net::netc as c;
-use crate::sys_common::net::LookupHost;
+use crate::sys::net::{LookupHost, netc as c};
 use crate::sys_common::{FromInner, IntoInner};
 use crate::{io, iter, mem, option, slice, vec};
 

std/src/net/tcp.rs

@@ -15,7 +15,8 @@ use crate::io::prelude::*;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::iter::FusedIterator;
 use crate::net::{Shutdown, SocketAddr, ToSocketAddrs};
-use crate::sys_common::{AsInner, FromInner, IntoInner, net as net_imp};
+use crate::sys::net as net_imp;
+use crate::sys_common::{AsInner, FromInner, IntoInner};
 use crate::time::Duration;
 
 /// A TCP stream between a local and a remote socket.