Upgrading .gitreview file for 1.7 branch

Change-Id: Id4fd211d62db1e11c8edb7caf8a979116aa39a69
diff --git a/.gitreview b/.gitreview
index 981cc4c..d8fe155 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,3 +3,4 @@
 port=29418
 project=olt.git
 defaultremote=origin
+defaultbranch=voltha-1.7