Fix NPE in Dhcp6Duid serializer

Change-Id: I0d367b3642efc69a4e036aac29f967718d16d841
diff --git a/utils/misc/src/main/java/org/onlab/packet/dhcp/Dhcp6Duid.java b/utils/misc/src/main/java/org/onlab/packet/dhcp/Dhcp6Duid.java
index 63be1f0..650b511 100644
--- a/utils/misc/src/main/java/org/onlab/packet/dhcp/Dhcp6Duid.java
+++ b/utils/misc/src/main/java/org/onlab/packet/dhcp/Dhcp6Duid.java
@@ -157,7 +157,7 @@
             case DUID_UUID:
                 byteBuffer = ByteBuffer.allocate(DEFAULT_UUID_LEN + uuid.length);
                 byteBuffer.putShort(duidType.value);
-                byteBuffer.put(linkLayerAddress);
+                byteBuffer.put(uuid);
                 break;
             default:
                 throw new IllegalArgumentException("Unknown duidType: " + duidType.toString());