ocfs2: Add ioctl for reflink.

The ioctl will take 3 parameters: old_path, new_path and
preserve and call vfs_reflink. It is useful when we backport
reflink features to old kernels.

Signed-off-by: Tao Ma <tao.ma@oracle.com>

fs/ocfs2/refcounttree.h

@@ -99,4 +99,8 @@ int ocfs2_increase_refcount(handle_t *handle,
 			    u64 cpos, u32 len,
 			    struct ocfs2_alloc_context *meta_ac,
 			    struct ocfs2_cached_dealloc_ctxt *dealloc);
+int ocfs2_reflink_ioctl(struct inode *inode,
+			const char __user *oldname,
+			const char __user *newname,
+			bool preserve);
 #endif /* OCFS2_REFCOUNTTREE_H */