doc: add more doc_cfg annotations (#1821)

Also makes the `tokio::net::{tcp, udp, unix}` modules only for "utility"
types. The primary types are in `tokio::net` directly.

2 files changed, 8 insertions, 13 deletions

diff --git a/tokio/src/net/udp/mod.rs b/tokio/src/net/udp/mod.rs
index b4d3ea46..a616f4d5 100644
--- a/tokio/src/net/udp/mod.rs
+++ b/tokio/src/net/udp/mod.rs
@@ -1,14 +1,7 @@
-//! UDP bindings for `tokio`.
-//!
-//! This module contains the UDP networking types, similar to the standard
-//! library, which can be used to implement networking protocols.
-//!
-//! The main struct for UDP is the [`UdpSocket`], which represents a UDP socket.
-//!
-//! [`UdpSocket`]: struct.UdpSocket
+//! UDP utility types.
 
-mod socket;
-pub use socket::UdpSocket;
+pub(crate) mod socket;
+pub(crate) use socket::UdpSocket;
 
 mod split;
 pub use split::{RecvHalf, SendHalf, ReuniteError};
diff --git a/tokio/src/net/udp/socket.rs b/tokio/src/net/udp/socket.rs
index 30cc104e..c22ebd92 100644
--- a/tokio/src/net/udp/socket.rs
+++ b/tokio/src/net/udp/socket.rs
@@ -9,9 +9,11 @@ use std::io;
 use std::net::{self, Ipv4Addr, Ipv6Addr, SocketAddr};
 use std::task::{Context, Poll};
 
-/// An I/O object representing a UDP socket.
-pub struct UdpSocket {
-    io: PollEvented<mio::net::UdpSocket>,
+cfg_udp! {
+    /// A UDP socket
+    pub struct UdpSocket {
+        io: PollEvented<mio::net::UdpSocket>,
+    }
 }
 
 impl UdpSocket {