TrafficTreatment: add support for IP DSCP modifications

Allow modifying IP DSCP field in the headers.

Change-Id: Idd765f40f1baec810273536adcd56bf0e480217f
diff --git a/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java b/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
index f61b017..154f8c6 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/TrafficTreatment.java
@@ -428,6 +428,14 @@
         Builder piTableAction(PiTableAction piTableAction);
 
         /**
+         * Sets the IP DSCP field.
+         *
+         * @param dscpValue the DSCP value
+         * @return a treatment builder.
+         */
+        Builder setIpDscp(byte dscpValue);
+
+        /**
          * Uses an extension treatment.
          *
          * @param extension extension treatment