fs: fsconfig: intercept non-new mount API in advance for FSCONFIG_CMD_CREATE_EXCL command

fsconfig with FSCONFIG_CMD_CREATE_EXCL command requires the new mount api,
here we should return -EOPNOTSUPP in advance to avoid extra procedure.

Signed-off-by: Hongbo Li <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/fsopen.c

···
 	if (!mount_capable(fc))
 		return -EPERM;
 
-	/* require the new mount api */
-	if (exclusive && fc->ops == &legacy_fs_context_ops)
-		return -EOPNOTSUPP;
-
 	fc->phase = FS_CONTEXT_CREATING;
 	fc->exclusive = exclusive;
 
···
 		case FSCONFIG_SET_PATH:
 		case FSCONFIG_SET_PATH_EMPTY:
 		case FSCONFIG_SET_FD:
+		case FSCONFIG_CMD_CREATE_EXCL:
 			ret = -EOPNOTSUPP;
 			goto out_f;
 		}