Implement the ethtool private statistics interface to expose additional
port-level and MAC-level counters that are not covered by the standard
IEEE 802.3 statistics. The pMAC counters are only reported when the port
supports Frame Preemption (802.1Qbu/802.3br).
Note that although rtnl_link_stats64 provides some standard statistics
such as rx octets, rx frame errors, rx dropped packets, and tx packets,
these are overall port statistics. The NETC switch supports preemption
on each port, and each port has two MACs (eMAC and pMAC). The driver
private statistics are used to obtain statistics for each MAC, allowing
users to perform analysis and debugging.