ONOS-6464 interfaces for protocol-independence (PI)

And also ONOS-6553, implementation of table entry classes

Change-Id: Ia7146b1bb0aac794e19b3fd8150c042e7ec70535
diff --git a/core/api/src/main/java/org/onosproject/net/flow/instructions/Instruction.java b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instruction.java
index 5c0353a..1aeb1d2 100644
--- a/core/api/src/main/java/org/onosproject/net/flow/instructions/Instruction.java
+++ b/core/api/src/main/java/org/onosproject/net/flow/instructions/Instruction.java
@@ -89,6 +89,11 @@
         L4MODIFICATION,
 
         /**
+         * Signifies that a protocol-independent instruction will be used.
+         */
+        PROTOCOL_INDEPENDENT,
+
+        /**
          * Signifies that an extension instruction will be used.
          */
         EXTENSION