Add JSON codec for ETH_DST_MASKED Criterion

- Enabling for a mcast flow rule to fetch its mask value from JSON dump

Change-Id: I8a69b0244dc332605d14e40998c329802a921286
(cherry picked from commit b62492324b4f913349ff7ed3e0ed3014b3f8f660)
diff --git a/core/common/src/main/java/org/onosproject/codec/impl/CriterionCodec.java b/core/common/src/main/java/org/onosproject/codec/impl/CriterionCodec.java
index 4be8008..24b749c 100644
--- a/core/common/src/main/java/org/onosproject/codec/impl/CriterionCodec.java
+++ b/core/common/src/main/java/org/onosproject/codec/impl/CriterionCodec.java
@@ -34,6 +34,7 @@
     static final String TYPE = "type";
     static final String ETH_TYPE = "ethType";
     static final String MAC = "mac";
+    static final String MAC_MASK = "macMask";
     static final String PORT = "port";
     static final String METADATA = "metadata";