Update to kernel with busy_poll support

diff --git a/kernel/3.12 b/kernel/3.12
index f6d51c347e2b35680619906000622401bf5f6cc5..d40550253b8ea0434100b496528b35759eff07e5 160000 (submodule)
--- a/kernel/3.12
+++ b/kernel/3.12
@@ -1 +1 @@
-Subproject commit f6d51c347e2b35680619906000622401bf5f6cc5
+Subproject commit d40550253b8ea0434100b496528b35759eff07e5