增加协议版本，新版本添加对gzip的支持

broker/src/main/java/io/moquette/persistence/MemorySessionStore.java

@@ -23,6 +23,7 @@ import io.moquette.spi.ClientSession;
 import io.moquette.spi.IMessagesStore.StoredMessage;
 import io.moquette.spi.ISessionsStore;
 
+import io.netty.handler.codec.mqtt.MqttVersion;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import cn.wildfirechat.common.ErrorCode;
@@ -49,6 +50,8 @@ public class MemorySessionStore implements ISessionsStore {
 
         private volatile int unReceivedMsgs;
 
+        private MqttVersion mqttVersion = MqttVersion.MQTT_3_1_1;
+
         public long getLastActiveTime() {
             return lastActiveTime;
         }
@@ -230,7 +233,13 @@ public class MemorySessionStore implements ISessionsStore {
 		}
 
 
-        
+        public MqttVersion getMqttVersion() {
+            return mqttVersion;
+        }
+
+        public void setMqttVersion(MqttVersion mqttVersion) {
+            this.mqttVersion = mqttVersion;
+        }
     }
 
     private final Map<String, Session> sessions = new ConcurrentHashMap<>();