Clarify comment when skipping binding to default exchange

It's not possible to bind to default exchange.

References #43 and #44.

Author: acogoluegnes

src/main/java/com/rabbitmq/perf/MulticastParams.java

@@ -292,7 +292,8 @@ public List<String> configureQueues(Connection connection, String id) throws IOE
                                      queueArguments).getQueue();
             }
             generatedQueueNames.add(qName);
-            // not allowed to bind to the default exchange
+            // skipping binding to default exchange,
+            // as it's not possible to explicitly bind to it.
             if (!"".equals(exchangeName) && !"amq.default".equals(exchangeName)) {
                 channel.queueBind(qName, exchangeName, id);
             }