[ONOS-3222] Implement toString method for each Packet class

Change-Id: I17d72338d4202117d08b3dca9463be35a87a0c1e
diff --git a/utils/misc/src/main/java/org/onlab/packet/IGMP.java b/utils/misc/src/main/java/org/onlab/packet/IGMP.java
index 254f132..594b79d 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IGMP.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IGMP.java
@@ -15,16 +15,19 @@
  */
 package org.onlab.packet;
 
+import org.slf4j.Logger;
+
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import org.slf4j.Logger;
+import java.util.Arrays;
 
-import static org.slf4j.LoggerFactory.getLogger;
+import static com.google.common.base.MoreObjects.toStringHelper;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static org.onlab.packet.PacketUtils.checkInput;
+import static org.slf4j.LoggerFactory.getLogger;
 
 
 /**
@@ -332,4 +335,15 @@
         result = prime * result + this.groups.hashCode();
         return result;
     }
+
+    @Override
+    public String toString() {
+        return toStringHelper(getClass())
+                .add("igmpType", Byte.toString(igmpType))
+                .add("resField", Byte.toString(resField))
+                .add("checksum", Short.toString(checksum))
+                .add("unsupportTypeData", Arrays.toString(unsupportTypeData))
+                .toString();
+        // TODO: need to handle groups
+    }
 }