SUNRPC: change cache_head.flags bits to enum

When a sequence of numbers are needed for internal-use only, an enum is
typically best.  The sequence will inevitably need to be changed one
day, and having an enum means the developer doesn't need to think about
renumbering after insertion or deletion.  Such patches will be easier
to review.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/cache.h

@@ -56,10 +56,14 @@ struct cache_head {
 	struct kref	ref;
 	unsigned long	flags;
 };
-#define	CACHE_VALID	0	/* Entry contains valid data */
-#define	CACHE_NEGATIVE	1	/* Negative entry - there is no match for the key */
-#define	CACHE_PENDING	2	/* An upcall has been sent but no reply received yet*/
-#define	CACHE_CLEANED	3	/* Entry has been cleaned from cache */
+
+/* cache_head.flags */
+enum {
+	CACHE_VALID,		/* Entry contains valid data */
+	CACHE_NEGATIVE,		/* Negative entry - there is no match for the key */
+	CACHE_PENDING,		/* An upcall has been sent but no reply received yet*/
+	CACHE_CLEANED,		/* Entry has been cleaned from cache */
+};
 
 #define	CACHE_NEW_EXPIRY 120	/* keep new things pending confirmation for 120 seconds */