locks: Allow disabling mandatory locking at compile time

Mandatory locking appears to be almost unused and buggy and there
appears no real interest in doing anything with it.  Since effectively
no one uses the code and since the code is buggy let's allow it to be
disabled at compile time.  I would just suggest removing the code but
undoubtedly that will break some piece of userspace code somewhere.

For the distributions that don't care about this piece of code
this gives a nice starting point to make mandatory locking go away.

Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jeff Layton <jeff.layton@primarydata.com>
Cc: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>

fs/Kconfig

@@ -67,6 +67,16 @@ config FILE_LOCKING
           for filesystems like NFS and for the flock() system
           call. Disabling this option saves about 11k.
 
+config MANDATORY_FILE_LOCKING
+	bool "Enable Mandatory file locking"
+	depends on FILE_LOCKING
+	default y
+	help
+	  This option enables files appropriately marked files on appropriely
+	  mounted filesystems to support mandatory locking.
+
+	  To the best of my knowledge this is dead code that no one cares about.
+
 source "fs/notify/Kconfig"
 
 source "fs/quota/Kconfig"