Report request queue length (or average waiting time)

[fvennetier]

Our network server has the ability to drop incoming requests when it is overbooked. The decision is made by comparing the time the request has spent in the incoming queue to the server.queue.max_delay configuration parameter (server/network_server.c).

We would like to report:

• the current length of the incoming request queue (g_thread_pool_unprocessed(srv->pool_tcp) may help);
• the average time a request waits in the queue.