[VOL-5245] - branch and release repo:voltha-lib-go

VERSION
.gitreview
----------
  o Update release .gitreview file, defaultbranch=voltha-2.12.

Change-Id: I8faffb210a406d37b2782fcb641897683fe9fa0a
diff --git a/.gitreview b/.gitreview
index b4f747a..8323c7a 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,4 +3,4 @@
 port=29418
 project=voltha-lib-go.git
 defaultremote=origin
-defaultbranch=master
+defaultbranch=voltha-2.12