stats: allow per second stats updates
Currently a special thread (CW) wakes up once per 3 second with the sole purpose to signal the other threads to sync their counters from the private store to the public store.
This is not configurable. The system will not take into account any threads that may be blocking due to no traffic.
It would be good to allow for more frequent stats synchronization so we can output (through logging or though unix socket) stats much more frequently. The system will have to take into account blocking capture and worker threads.