per-socket statistics

Think twice before you pick the source of information about network behaviour…Especially, /proc/$PID/net and friends are _not_ process-dependent as you might think. At least, not until your process got a dedicated _namespace_ to work with. So yes, every `struct sock` has a sk_net field that eventually leads to some statistics (`sock->sk_net->mib.net_statistics`), but if you look …