Added symbolic names with the correct values for
PIM Address families IPv4 and IPv6

Change-Id: I8ae675fa1df052c4ef0b73b27449add534cc5c3c
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 d9a5e83..e6ef0ae 100755
--- a/utils/misc/src/main/java/org/onlab/packet/PIM.java
+++ b/utils/misc/src/main/java/org/onlab/packet/PIM.java
@@ -43,6 +43,9 @@
 
     public static final int PIM_HEADER_LEN = 4;
 
+    public static final byte ADDRESS_FAMILY_IP4 = 0x1;
+    public static final byte ADDRESS_FAMILY_IP6 = 0x2;
+
     public static final Map<Byte, Deserializer<? extends IPacket>> PROTOCOL_DESERIALIZER_MAP =
             new HashMap<>();