aio/unix: Use signal.sival which is standard

[Sergey Kandaurov]

> On 8 Jan 2019, at 06:37, Sepherosa Ziehau <sepherosa at gmail.com> wrote:
> 
> sigval.sigval is for FreeBSD 6 compability, while FreeBSD 6 was EOL
> for quite a while.
> 
> Patch:
> https://leaf.dragonflybsd.org/~sephe/nginx_sival.diff

Committed in 7f035fd1ec7b (with changes), thanks.

-- 
Sergey Kandaurov