audit: add header protection to kernel/audit.h

Protect kernel/audit.h against multiple #include's.
Signed-off-by: MaYuming <mayuming77@hotmail.com>
[PM: rewrite subj/description]
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit.h

@@ -6,6 +6,9 @@
  * Copyright 2005 IBM Corporation
  */
 
+#ifndef _KERNEL_AUDIT_H_
+#define _KERNEL_AUDIT_H_
+
 #include <linux/fs.h>
 #include <linux/audit.h>
 #include <linux/skbuff.h>
@@ -331,3 +334,5 @@ extern int audit_filter(int msgtype, unsigned int listtype);
 
 extern void audit_ctl_lock(void);
 extern void audit_ctl_unlock(void);
+
+#endif