add a new module to handle failed vBNG requests

 If the vBNG manager failed to create a vBNG for a private IP address
 for the first time, usurally because the next hop host or host configured
 with private IP address is not in the ONOS system. During the first time
 to create a vBNG, if such case happens, vBNG manager will send out the
 probe packets to try to find those hosts.

 Thus, we should try to create vBNG again after the probe packets.

Change-Id: Ib8684602d4f761d2d09ac8d93738120aa57ce225
diff --git a/apps/virtualbng/src/main/java/org/onosproject/virtualbng/VbngConfigurationService.java b/apps/virtualbng/src/main/java/org/onosproject/virtualbng/VbngConfigurationService.java
index 4a539f0..644c229 100644
--- a/apps/virtualbng/src/main/java/org/onosproject/virtualbng/VbngConfigurationService.java
+++ b/apps/virtualbng/src/main/java/org/onosproject/virtualbng/VbngConfigurationService.java
@@ -36,4 +36,12 @@
      * @return an available public IP address if it exists, otherwise null
      */
     public IpAddress getAvailablePublicIpAddress(IpAddress privateIpAddress);
+
+    /**
+     * Gets the public IP address already assigned for a private IP address.
+     *
+     * @param privateIpAddress a private IP address
+     * @return the assigned public IP address if it exists, otherwise null
+     */
+    public IpAddress getAssignedPublicIpAddress(IpAddress privateIpAddress);
 }