Define a Criterion for OchSginalType

Resolve ONOS-1846

Change-Id: I63462a3e2702c93b1d1c84a324bdbaa351bac633
diff --git a/core/api/src/main/java/org/onosproject/net/flow/criteria/Criteria.java b/core/api/src/main/java/org/onosproject/net/flow/criteria/Criteria.java
index be4b90d..6e9a228 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/criteria/Criteria.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/criteria/Criteria.java
@@ -25,6 +25,7 @@
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.MplsLabel;
 import org.onlab.packet.VlanId;
+import org.onosproject.net.tunnel.OchSignalType;
 
 /**
  * Factory class to create various traffic selection criteria.
@@ -391,6 +392,16 @@
         return new OpticalSignalTypeCriterion(sigType, Type.OCH_SIGTYPE);
     }
 
+    /**
+     * Create a match on OCh (Optical Channel) signal type.
+     *
+     * @param signalType OCh signal type
+     * @return match criterion
+     */
+    public static Criterion matchOchSignalType(OchSignalType signalType) {
+        return new OchSignalTypeCriterion(signalType);
+    }
+
     public static Criterion dummy() {
         return new DummyCriterion();
     }