Initialise the Window network stack in one call site

Do it in new_socket so that the higher levels don't have to worry about
it.

src/sys/windows/net.rs

@@ -9,7 +9,7 @@ use windows_sys::Win32::Networking::WinSock::{
 };
 
 /// Initialise the network stack for Windows.
-pub(crate) fn init() {
+fn init() {
     static INIT: Once = Once::new();
     INIT.call_once(|| {
         // Let standard library call `WSAStartup` for us, we can't do it
@@ -30,6 +30,8 @@ pub(crate) fn new_ip_socket(addr: SocketAddr, socket_type: u16) -> io::Result<SO
 }
 
 pub(crate) fn new_socket(domain: u32, socket_type: u16) -> io::Result<SOCKET> {
+    init();
+
     syscall!(
         socket(domain as i32, socket_type as i32, 0),
         PartialEq::eq,

src/sys/windows/tcp.rs

@@ -2,19 +2,12 @@ use std::io;
 use std::net::{self, SocketAddr};
 use std::os::windows::io::AsRawSocket;
 
-use windows_sys::Win32::Networking::WinSock::{
-    self, AF_INET, AF_INET6, SOCKET, SOCKET_ERROR, SOCK_STREAM,
-};
+use windows_sys::Win32::Networking::WinSock::{self, SOCKET, SOCKET_ERROR, SOCK_STREAM};
 
-use crate::sys::windows::net::{init, new_socket, socket_addr};
+use crate::sys::windows::net::{new_ip_socket, socket_addr};
 
 pub(crate) fn new_for_addr(address: SocketAddr) -> io::Result<SOCKET> {
-    init();
-    let domain = match address {
-        SocketAddr::V4(_) => AF_INET,
-        SocketAddr::V6(_) => AF_INET6,
-    };
-    new_socket(domain, SOCK_STREAM)
+    new_ip_socket(address, SOCK_STREAM)
 }
 
 pub(crate) fn bind(socket: &net::TcpListener, addr: SocketAddr) -> io::Result<()> {

src/sys/windows/udp.rs

@@ -4,13 +4,12 @@ use std::net::{self, SocketAddr};
 use std::os::windows::io::{AsRawSocket, FromRawSocket};
 use std::os::windows::raw::SOCKET as StdSocket; // windows-sys uses usize, stdlib uses u32/u64.
 
-use crate::sys::windows::net::{init, new_ip_socket, socket_addr};
+use crate::sys::windows::net::{new_ip_socket, socket_addr};
 use windows_sys::Win32::Networking::WinSock::{
     bind as win_bind, closesocket, getsockopt, IPPROTO_IPV6, IPV6_V6ONLY, SOCKET_ERROR, SOCK_DGRAM,
 };
 
 pub fn bind(addr: SocketAddr) -> io::Result<net::UdpSocket> {
-    init();
     new_ip_socket(addr, SOCK_DGRAM).and_then(|socket| {
         let (raw_addr, raw_addr_length) = socket_addr(&addr);
         syscall!(