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

[Maurizio Lombardi]

On Fri Mar 28, 2025 at 10:24 AM CET, zhang.guanghui at cestc.cn wrote:
> Hi, 
>
>       So far,  the UAF issue have not been occcurred during testing this patch in the same situation. 
> Additionally, the patch triggers a compilation warning,  nvme_tcp_fail_request is declared but not defined, please also review.  
>

Ok, I am going to submit a formal patch.

Thanks for testing it,
Maurizio