ceph: move readahead default to fs/ceph from libceph

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 5405c903..619fe71 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -36,6 +36,7 @@
 #define ceph_test_mount_opt(fsc, opt) \
 	(!!((fsc)->mount_options->flags & CEPH_MOUNT_OPT_##opt))
 
+#define CEPH_RSIZE_DEFAULT             (512*1024) /* readahead */
 #define CEPH_MAX_READDIR_DEFAULT        1024
 #define CEPH_MAX_READDIR_BYTES_DEFAULT  (512*1024)
 #define CEPH_SNAPDIRNAME_DEFAULT        ".snap"