fix(igd): Fix the condition for terminating the IGD renewal loop

The condition was the wrong way around. The desired behaviour is that
closing an endpoint causes the renewal loop to stop. When an endpoint
is closed, a message (`()`) is sent to the `termination_tx`, which is
connected to the `termination_rx` in the renewal loop. Therefore we want
to break the loop if we *have* received a message, indicating that the
endpoint was closed.

The condition would also terminate the loop on any other error from
`try_recv` (e.g. if the endpoint was dropped), and this has been
preserved.

src/igd.rs

@@ -32,7 +32,7 @@ pub async fn forward_port(
 
             loop {
                 let _ = timer.tick().await;
-                if let Err(TryRecvError::Empty) = termination_rx.try_recv() {
+                if termination_rx.try_recv() != Err(TryRecvError::Empty) {
                     break;
                 }
                 debug!("Renewing IGD lease for port {}", local_addr);