Update kernel headers to v3.18.3.

Bug: 19127803
Change-Id: I67fa0832322ddd0032d909476047578be052bcf2
diff --git a/libc/kernel/uapi/linux/kernel-page-flags.h b/libc/kernel/uapi/linux/kernel-page-flags.h
index c4d05cc..ce30be7 100644
--- a/libc/kernel/uapi/linux/kernel-page-flags.h
+++ b/libc/kernel/uapi/linux/kernel-page-flags.h
@@ -47,4 +47,5 @@
 #define KPF_KSM 21
 /* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
 #define KPF_THP 22
+#define KPF_BALLOON 23
 #endif