netstack: remove timed-out endpoints from pendingEndpoints queue.

When a handshake times out, the endpoint may remain stuck in the lEP's pendingEndpoints queue.

Related to google#11536

Author: JiaHuann

pkg/tcpip/transport/tcp/endpoint.go

@@ -1193,6 +1193,14 @@ func (e *Endpoint) cleanupLocked() {
 		e.timeWaitTimer.Stop()
 	}
 
+	// Remove current EP from its lEP acceptQueue.pendingEndpoint if exists.
+	if e.h != nil && e.h.listenEP != nil {
+		lEP := e.h.listenEP
+		lEP.acceptMu.Lock()
+		delete(lEP.acceptQueue.pendingEndpoints, e)
+		lEP.acceptMu.Unlock()
+	}
+
 	// Close all endpoints that might have been accepted by TCP but not by
 	// the client.
 	e.closePendingAcceptableConnectionsLocked()