Always reset agent connection backoff and enter fast sync when client count < server count (#632)

* Always reset backoff and enter fast sync when clien count < server count

* Only call ClientsCount() once

* Review comment

Author: carreter

pkg/agent/clientset.go

@@ -183,9 +183,13 @@ func (cs *ClientSet) sync() {
 	for {
 		if err := cs.connectOnce(); err != nil {
 			if dse, ok := err.(*DuplicateServerError); ok {
-				klog.V(4).InfoS("duplicate server", "serverID", dse.ServerID, "serverCount", cs.serverCount, "clientsCount", cs.ClientsCount())
-				if cs.serverCount != 0 && cs.ClientsCount() >= cs.serverCount {
+				clientsCount := cs.ClientsCount()
+				klog.V(4).InfoS("duplicate server", "serverID", dse.ServerID, "serverCount", cs.serverCount, "clientsCount", clientsCount)
+				if cs.serverCount != 0 && clientsCount >= cs.serverCount {
 					duration = backoff.Step()
+				} else {
+					backoff = cs.resetBackoff()
+					duration = wait.Jitter(backoff.Duration, backoff.Jitter)
 				}
 			} else {
 				klog.ErrorS(err, "cannot connect once")