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

@@ -1156,6 +1156,14 @@ func (e *Endpoint) closePendingAcceptableConnectionsLocked() {
 	pendingEndpoints := e.acceptQueue.pendingEndpoints
 	e.acceptQueue.pendingEndpoints = nil
 
+	//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()
+	}
+
 	completedEndpoints := make([]*Endpoint, 0, e.acceptQueue.endpoints.Len())
 	for n := e.acceptQueue.endpoints.Front(); n != nil; n = n.Next() {
 		completedEndpoints = append(completedEndpoints, n.Value.(*Endpoint))