107e3b6851
BridgeDevice STP hardening: - send(): check STP blocking before unicast forwarding (host-originated) - recv(): check STP blocking before unicast forwarding (switched frames) - Previously only flood() checked STP; unicast forwarding bypassed it. A blocked port must never forward any traffic — STP semantics now correct. netcfg stats enhancement: - Per-interface stats now include mtu= and link= fields alongside counters - Applies to both eth0 and loopback - Enables bandwidth monitoring tools to self-discover MTU/link state