server socket SO_REUSEPORT option

From linux kernel >= 3.9, socket support so_reuseport option, With the SO_REUSEPORT option enabled, there are multiple socket listeners for each IP address and port combination, one for each worker process. The kernel determines which available socket listener (and by implication, which worker) gets the connection. This can reduce lock contention between workers accepting new connections, and improve performance on multicore systems. However, it can also mean that when a worker is stalled by a blocking operation, the block affects not only connections that the worker has already accepted, but also connection requests that the kernel has assigned to the worker since it became blocked.

Nova-api dependes on subprocess and green thread, if it use SO_REUSEPORT option, it will good to process request.