net/handshake: restore destructor on submit failure

In the Linux kernel, the following vulnerability has been resolved:

net/handshake: restore destructor on submit failure

handshake_req_submit() replaces sk->sk_destruct but never restores it when submission fails before the request is hashed. handshake_sk_destruct() then returns early and the original destructor never runs, leaking the socket. Restore sk_destruct on the error path.