vsock: remove ratelimit unknown ioctl message

When exercising the kernel with stress-ng with some ioctl tests the
"Unknown ioctl" error message is spamming the kernel log at a high
rate. Remove this message.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>