Fix possible mem leak in fsocket_spawn_clone.

1. Add the lost fsock_free_sock in some error handlers in fsocket_spawn_clone.
2. Rollback the update bb4d2fec21fea6feeba2c6a3e36df0b5b4894aa7.
   Actually the __fsocket_filp_close will free the sock. So need not invoke fsock_free_sock again.