Improvided PIM Hello option handling by creating the
PIMHelloOption class.  Also fixed a typo for pim regsiter
stop message type.

Change-Id: Iff06ce7d2746ebc34811205f4c4a4d4784e2740c
diff --git a/utils/misc/src/main/java/org/onlab/packet/PIM.java b/utils/misc/src/main/java/org/onlab/packet/PIM.java
index d306263..d9a5e83 100755
--- a/utils/misc/src/main/java/org/onlab/packet/PIM.java
+++ b/utils/misc/src/main/java/org/onlab/packet/PIM.java
@@ -33,7 +33,7 @@
 
     public static final byte TYPE_HELLO = 0x00;
     public static final byte TYPE_REGISTER = 0x01;
-    public static final byte TYPE_REQUEST_STOP = 0x02;
+    public static final byte TYPE_REGISTER_STOP = 0x02;
     public static final byte TYPE_JOIN_PRUNE_REQUEST = 0x03;
     public static final byte TYPE_BOOTSTRAP = 0x04;
     public static final byte TYPE_ASSERT = 0x05;