fix log message

Change-Id: Ia46b5ad2564bff37bf344938809c61960d1930c3

@@ -104,7 +104,7 @@ public final class DefaultOpenFlowPacketContext implements OpenFlowPacketContext
         } catch (BufferUnderflowException | NullPointerException |
         } catch (BufferUnderflowException | NullPointerException |
                 DeserializationException e) {
                 DeserializationException e) {
             Logger log = LoggerFactory.getLogger(getClass());
             Logger log = LoggerFactory.getLogger(getClass());
-            log.warn("packet deserialization problem : {}", e.getMessage());
+            log.error("packet deserialization problem : {}", e.getMessage());
             return null;
             return null;
         }
         }
     }
     }