nvme-tcp: fix a possible UAF when failing to send request

[Maurizio Lombardi]

On Wed Feb 12, 2025 at 9:11 AM CET, Maurizio Lombardi wrote:
> Hello, could you try this patch?
>
> Concurrent calls to try_recv() should already be protected by
> sock_lock.
>
> +	mutex_lock(&queue->send_mutex);
>  	nvme_tcp_try_recv(queue);
> +	r = queue->nr_cqe;
> +	mutex_unlock(&queue->send_mutex);

Well, reading nr_cqe like this is still racy, but should be a minor
issue and not hard to fix.

Maurizio