fuse: add renameat2 support

Support RENAME_EXCHANGE and RENAME_NOREPLACE flags on the userspace ABI.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/fuse_i.h

@@ -542,6 +542,9 @@ struct fuse_conn {
 	/** Is fallocate not implemented by fs? */
 	unsigned no_fallocate:1;
 
+	/** Is rename with flags implemented by fs? */
+	unsigned no_rename2:1;
+
 	/** Use enhanced/automatic page cache invalidation. */
 	unsigned auto_inval_data:1;