Revert ":s/master/koala/" in master

This reverts commit ec6b87b30e658dfd6cdd9c93941d2d87e53f9ad1.
diff --git a/default.xml b/default.xml
index 5d9940d..6af8c04 100644
--- a/default.xml
+++ b/default.xml
@@ -4,7 +4,7 @@
     fetch="https://gfiber-internal.googlesource.com/"
     name="gfiber-internal"
     review="https://gfiber-internal-review.googlesource.com/"/>
-  <default remote="gfiber-internal" revision="koala" sync-j="12"/>
+  <default remote="gfiber-internal" revision="master" sync-j="12"/>
 
   <project name="manifests" path="manifest"/>
   <project name="toolchains/bruno"/>