net: implement IntoRawFd for TcpSocket (#3684)

tokio/src/net/tcp/socket.rs

@@ -5,7 +5,7 @@ use std::io;
 use std::net::SocketAddr;
 
 #[cfg(unix)]
-use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
 #[cfg(windows)]
 use std::os::windows::io::{AsRawSocket, FromRawSocket, IntoRawSocket, RawSocket};
 
@@ -511,6 +511,13 @@ impl FromRawFd for TcpSocket {
     }
 }
 
+#[cfg(unix)]
+impl IntoRawFd for TcpSocket {
+    fn into_raw_fd(self) -> RawFd {
+        self.inner.into_raw_fd()
+    }
+}
+
 #[cfg(windows)]
 impl IntoRawSocket for TcpSocket {
     fn into_raw_socket(self) -> RawSocket {