ONOS-2581 Add codec for tunnel id

Change-Id: I6ff456b0419b427945cc53fb74fd0a91cdfa758e
diff --git a/core/common/src/main/java/org/onosproject/codec/impl/EncodeInstructionCodecHelper.java b/core/common/src/main/java/org/onosproject/codec/impl/EncodeInstructionCodecHelper.java
index 850334d..6927680 100644
--- a/core/common/src/main/java/org/onosproject/codec/impl/EncodeInstructionCodecHelper.java
+++ b/core/common/src/main/java/org/onosproject/codec/impl/EncodeInstructionCodecHelper.java
@@ -123,6 +123,12 @@
                            pushHeaderInstructions.ethernetType().toShort());
                 break;
 
+            case TUNNEL_ID:
+                final L2ModificationInstruction.ModTunnelIdInstruction modTunnelIdInstruction =
+                        (L2ModificationInstruction.ModTunnelIdInstruction) instruction;
+                result.put(InstructionCodec.TUNNEL_ID, modTunnelIdInstruction.tunnelId());
+                break;
+
             default:
                 log.info("Cannot convert L2 subtype of {}", instruction.subtype());
                 break;