VOL-1834 Report when tagging is not as expected

Change-Id: I863fb1786f9355314088dcfc9f0fe697a6932403
diff --git a/core/io_worker.go b/core/io_worker.go
index 00ecda3..e0ffd10 100644
--- a/core/io_worker.go
+++ b/core/io_worker.go
@@ -85,8 +85,7 @@
 			return retpkt, vid, nil
 		}
 	}
-	return pkt, 0, nil
-	// return nil, 0, errors.New("failed to pop vlan")
+	return nil, 0, errors.New("failed to pop vlan")
 }
 
 // PushVLAN pushes the vlan header to the packet and returns tha packet