Real-NE2000 semantics: accept only own-MAC unicast + broadcast (multicast
excluded -- the guest stack is unicast+ARP only), and drop npcap's loopback
of our own injected frames. Without it, a live-LAN host download floods the
emulated NIC at wire rate (65k+ frames/min) and wedges netnub before boot
("discarding..."). Filter failure is non-fatal: logs and runs unfiltered.
Also log the first 12 unicast accepts/drops with the live PAR registers.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>