Expose more network statistics for containers on CNI network in the `network/cni` isolator.

This is a second step after MESOS-5647. We need to expose more networking metrics for containers on CNI network in the `network/cni` isolator. At the moment `usage()` method calls `getifaddrs(3)` to get limited statistics such as received/transmitted bytes, packets, errors and dropped packets. It works on any modern linux-based system. `usage()` method could use Netlink Protocol Library to get more metrics and expose it into `ResourceStatistics`. Please create the netlink socket in the corresponding network namespace through the `NamespaceRunner` and re-use the socket in `usage()`.