nova: kernel warnings during run/init_smp

```
[2025-06-26 06:22:53] [ 0] invalid state, still have xcpu_sm
```

This message may appear if a thread  in a cross core IPC is destructed. The output collides with the output of the Genode test (run/init_smp) so that the test is marked as failed, even so it finished successfully. The message hints for a potential memory leak during destruction of a thread.