Move getCurrentTimeMillis() to abstract class and changed access modified to protected

common/transport/transport-api/src/main/java/org/thingsboard/server/common/transport/service/DefaultTransportService.java

@@ -775,10 +775,6 @@ public class DefaultTransportService extends TransportActivityManager implements
         onActivity(toSessionId(sessionInfo), getCurrentTimeMillis());
     }
 
-    long getCurrentTimeMillis() {
-        return System.currentTimeMillis();
-    }
-
     @Override
     public void lifecycleEvent(TenantId tenantId, DeviceId deviceId, ComponentLifecycleEvent eventType, boolean success, Throwable error) {
         ToCoreMsg msg = ToCoreMsg.newBuilder()

common/transport/transport-api/src/main/java/org/thingsboard/server/common/transport/service/TransportActivityManager.java

@@ -142,7 +142,7 @@ public abstract class TransportActivityManager extends AbstractActivityManager<U
         });
     }
 
-    long getCurrentTimeMillis() {
+    protected long getCurrentTimeMillis() {
         return System.currentTimeMillis();
     }