fs: reserve fallocate flag codepoint

As discussed at the Plumber's Conference, reserve the bit 0x04 in
fallocate() to prevent collisions with a commonly used out-of-tree
patch which implements the no-hide-stale feature.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

include/linux/falloc.h

@@ -3,6 +3,7 @@
 
 #define FALLOC_FL_KEEP_SIZE	0x01 /* default is extend size */
 #define FALLOC_FL_PUNCH_HOLE	0x02 /* de-allocates range */
+#define FALLOC_FL_NO_HIDE_STALE	0x04 /* reserved codepoint */
 
 #ifdef __KERNEL__