Return TCP listener errors. (#1218)

* Add listener ID and error event.

Report listener errors to client code so they are aware that an error
occurred within a listener. By default we continue to poll listeners
which produced an error, but clients can remove listeners by ID.

* tcp: Report errors.

Instead of silently waiting after errors we return all errors, but pause
after each error, before continuing.

* Add a test.

To ease testing, `Listener` is made generic and we test that no values
and errors are lost. Elapsed time between item generation is not
measured.

* Support the new methods in core-derive.

* Address review concerns.

* Remove `Display` impl of `ListenerId`.

* Add 'static bound to `on_listener_error` error.

swarm/src/behaviour.rs

@@ -19,7 +19,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 use crate::protocols_handler::{IntoProtocolsHandler, ProtocolsHandler};
-use libp2p_core::{ConnectedPoint, Multiaddr, PeerId};
+use libp2p_core::{ConnectedPoint, Multiaddr, PeerId, nodes::ListenerId};
 use futures::prelude::*;
 use std::error;
 
@@ -121,6 +121,14 @@ pub trait NetworkBehaviour {
     fn inject_new_external_addr(&mut self, _addr: &Multiaddr) {
     }
 
+    /// A listener experienced an error.
+    fn inject_listener_error(&mut self, _id: ListenerId, _err: &(dyn std::error::Error + 'static)) {
+    }
+
+    /// A listener closed.
+    fn inject_listener_closed(&mut self, _id: ListenerId) {
+    }
+
     /// Polls for things that swarm should do.
     ///
     /// This API mimics the API of the `Stream` trait. The method may register the current task in