cobalt/drivers: Ensure bidirectional IOCTL migration

Ensure that IOCTL switch-over is also prepared for the NRT-to-RT path.
While we didn't need this in practice for the changed drivers, it's
better to have this enabled in case driver developers derive from this
pattern.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kernel/drivers/autotune/autotune.c

@@ -665,7 +665,7 @@ static int autotune_ioctl_nrt(struct rtdm_fd *fd, unsigned int request, void *ar
 		tuner = &uthread_tuner.tuner;
 		break;
 	default:
-		return -EINVAL;
+		return -ENOSYS;
 	}
 
 	ret = rtdm_copy_from_user(fd, &setup, arg, sizeof(setup));

kernel/drivers/testing/switchtest.c

@@ -667,7 +667,7 @@ static int rtswitch_ioctl_nrt(struct rtdm_fd *fd,
 		return 0;
 
 	default:
-		return -ENOTTY;
+		return -ENOSYS;
 	}
 }
 

kernel/drivers/testing/timerbench.c

@@ -453,7 +453,7 @@ static int rt_tmbench_ioctl_nrt(struct rtdm_fd *fd,
 		err = rt_tmbench_stop(ctx, arg);
 		break;
 	default:
-		err = -EINVAL;
+		err = -ENOSYS;
 	}
 
 	return err;