ceph: fix incorrect old_size length in ceph_mds_request_args

The 'old_size' is a __le64 type since birth, not sure why the
kclient incorrectly switched it to __le32. This change is okay
won't break anything because union will always allocate more memory
than the 'open' member needed.

Rename 'file_replication' to 'pool' as ceph did. Though this 'open'
struct may never be used in kclient in future, it's confusing when
going through the ceph code.

Signed-off-by: Xiubo Li <[e-mail]>
Reviewed-by: Ilya Dryomov <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>

include/linux/ceph/ceph_fs.h

···
 		__le32 stripe_unit;          /* layout for newly created file */
 		__le32 stripe_count;         /* ... */
 		__le32 object_size;
-		__le32 file_replication;
-               __le32 mask;                 /* CEPH_CAP_* */
-               __le32 old_size;
+		__le32 pool;
+		__le32 mask;                 /* CEPH_CAP_* */
+		__le64 old_size;
 	} __attribute__ ((packed)) open;
 	struct {
 		__le32 flags;