thread safe improvment

Change-Id: I09b6dc7a3003792ec975b5b8c8c423d38d65767b

@@ -112,7 +112,8 @@ public class VbngConfigurationManager implements VbngConfigurationService {
     // TODO handle the case: the number of public IP addresses is not enough
     // for 1:1 mapping from public IP to private IP.
     @Override
-    public IpAddress getAvailablePublicIpAddress(IpAddress privateIpAddress) {
+    public synchronized IpAddress getAvailablePublicIpAddress(IpAddress
+                                                           privateIpAddress) {
         // If there is already a mapping entry for the private IP address,
         // then fetch the public IP address in the mapping entry and return it.
         IpAddress publicIpAddress = ipAddressMap.get(privateIpAddress);

@@ -47,10 +47,8 @@ public class VbngResource extends BaseResource {
         VbngService vbngService = get(VbngService.class);
 
         IpAddress publicIpAddress = null;
-        synchronized (this) {
-            // Create a virtual BNG
-            publicIpAddress = vbngService.createVbng(privateIpAddress);
-        }
+        // Create a virtual BNG
+        publicIpAddress = vbngService.createVbng(privateIpAddress);
 
         if (publicIpAddress != null) {
             return publicIpAddress.toString();