In some cases, for example, packets are forwarded to your server through
IP tunnel, and they will be received on fixed queues, since RSS doesn't support tunnels.So we need to dispatch them again.
With this commit, we can implement a dispatcher callback function and regist
it, packets retrieved from rx queue will be dispatched again according to
the dispatcher result.
Since f-stack run with polling mode, nginx will call gettimeofday every loop, and cost a lot.
With this commit, f-stack will update current timespec periodically in
ff_hardclock_job. And ff_gettimeofday will get this value.
In nginx, hijack gettimeofday to call ff_gettimeofday.