Fixing MEF whitepaper link

Change-Id: I152762c07b38f984972c87674c2065d92babad51
diff --git a/.gitreview b/.gitreview
index 84dc7a2..20fb249 100644
--- a/.gitreview
+++ b/.gitreview
@@ -3,3 +3,4 @@
 port=29418
 project=openolt.git
 defaultremote=origin
+defaultbranch=voltha-2.6