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

Change-Id: I17d72338d4202117d08b3dca9463be35a87a0c1e
diff --git a/utils/misc/src/main/java/org/onlab/packet/ICMP6.java b/utils/misc/src/main/java/org/onlab/packet/ICMP6.java
index c898130..45b7a62 100644
--- a/utils/misc/src/main/java/org/onlab/packet/ICMP6.java
+++ b/utils/misc/src/main/java/org/onlab/packet/ICMP6.java
@@ -29,6 +29,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import static com.google.common.base.MoreObjects.toStringHelper;
 import static org.onlab.packet.PacketUtils.checkInput;
 
 /**
@@ -363,4 +364,13 @@
             return icmp6;
         };
     }
+
+    @Override
+    public String toString() {
+        return toStringHelper(getClass())
+                .add("icmpType", Byte.toString(icmpType))
+                .add("icmpCode", Byte.toString(icmpCode))
+                .add("checksum", Short.toString(checksum))
+                .toString();
+    }
 }