net: add TcpSocket::take_error (#4364)

Author: taiki-e

tokio/src/net/tcp/socket.rs

@@ -409,6 +409,11 @@ impl TcpSocket {
             .map(|addr| addr.as_socket().unwrap())
     }
 
+    /// Returns the value of the `SO_ERROR` option.
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.inner.take_error()
+    }
+
     /// Binds the socket to the given address.
     ///
     /// This calls the `bind(2)` operating-system function. Behavior is