Bridge: statistics() aggregates rx/tx bytes+packets from all member ports.
arp_stats() delegates to each port, showing per-port breakdown.
Bond: statistics() aggregates from all slaves (active+standby).
arp_stats() delegates to each slave.
TUN: statistics() now returns live counters tracked during send()/recv().
rx_bytes, rx_packets, tx_bytes, tx_packets increment per-packet.
Previously these devices returned Stats::default() (all zeros).
Now netcfg /ifaces/*/stats shows real data for bridge, bond, tun.