Switching from fabric-tna master to main

Change-Id: I205efd5f7326022372d36c35602ae2f584677372
diff --git a/Makefile.vars.master b/Makefile.vars.master
index d160578..e79841a 100644
--- a/Makefile.vars.master
+++ b/Makefile.vars.master
@@ -32,4 +32,4 @@
 export FABRIC_TOFINO_VERSION   ?= master
 export UP4_VERSION             ?= master
 export KAFKA_ONOS_VERSION      ?= 2.6.0-SNAPSHOT
-export FABRIC_TNA_VERSION      ?= master
+export FABRIC_TNA_VERSION      ?= main