Support STT tunneling protocol at kubevirt networking app

Change-Id: Icbef76dbfb842ce1cf6893bf18ee80c4b1b26006
diff --git a/core/api/src/main/java/org/onosproject/net/behaviour/TunnelDescription.java b/core/api/src/main/java/org/onosproject/net/behaviour/TunnelDescription.java
index 4d9e41b..d53ab93 100644
--- a/core/api/src/main/java/org/onosproject/net/behaviour/TunnelDescription.java
+++ b/core/api/src/main/java/org/onosproject/net/behaviour/TunnelDescription.java
@@ -54,6 +54,10 @@
          */
         GENEVE,
         /**
+         * Signifies that this is a L3 tunnel.
+         */
+        STT,
+        /**
          * Signifies that this is a L1 OTN tunnel.
          */
         ODUK,