[VOL-5247] tag repo:voltha-go for release

VERSION
.gitreview
----------
    o Bump version string for the release tag

Change-Id: I658c7066201caf8d3fd96b15a9bfcf90230016a5
diff --git a/.gitreview b/.gitreview
index c70a26b..6ba4e7b 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,3 +3,4 @@
 port=29418
 project=voltha-go.git
 defaultremote=origin
+defaultbranch=voltha-2.12