ceph: move max constant definitions

Move some definitions for max integer values out of the rbd code and
into the more central "decode.h" header file.  These really belong
in a Linux (or libc) header somewhere, but I haven't gotten around
to proposing that yet.

This is in preparation for moving some code out of rbd.c and into
the osd client.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

include/linux/ceph/decode.h

@@ -8,6 +8,13 @@
 
 #include <linux/ceph/types.h>
 
+/* This seemed to be the easiest place to define these */
+
+#define	U8_MAX	((u8)  (~0U))
+#define	U16_MAX	((u16) (~0U))
+#define	U32_MAX	((u32) (~0U))
+#define	U64_MAX	((u64) (~0ULL))
+
 /*
  * in all cases,
  *   void **p     pointer to position pointer