Revert "grouper: update prebuilt kernel"

This reverts commit 3bf293441fa11bdd9dc94eb3f951b368669e884b.

This commit accidentally overwrote subsequent kernel changes and should
not have been merged.
diff --git a/kernel b/kernel
index fc3a2b0..1aa73da 100644
--- a/kernel
+++ b/kernel
Binary files differ