Switch manifest to stabilized kernel build tools

The 'master-kernel-build-2021' branch is a pinned version of the master
branch that is not receiving any new features and is therefore to be
used for non-development branches.

Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: I17d713265be5661c6bdd20ed0656fe1263cd8ada
diff --git a/default.xml b/default.xml
index 5817ea7..a15be23 100644
--- a/default.xml
+++ b/default.xml
@@ -1,7 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <manifest>
   <remote  name="aosp" fetch=".." review="https://android-review.googlesource.com/" />
-  <default revision="master" remote="aosp" sync-j="4" />
+  <default revision="master-kernel-build-2021" remote="aosp" sync-j="4" />
+
   <project path="build" name="kernel/build" />
   <project path="common" name="kernel/common" revision="android-4.9-q" />
   <project path="kernel/tests" name="kernel/tests" />