add get description to PrivateGatewayProfile

Author: charlesweng

server/src/main/java/com/cloud/network/vpc/PrivateGatewayProfile.java

@@ -81,6 +81,11 @@ public String getNetmask() {
         return vpcGateway.getNetmask();
     }
 
+    @Override
+    public String getDescription() {
+        return vpcGateway.getDescription();
+    }
+
     @Override
     public long getPhysicalNetworkId() {
         return physicalNetworkId;