08938e304b
EthernetLink gains ARP_CACHE_MAX = 1024 constant and insert_neighbor(ip, hw, now) helper. When the cache reaches the limit and the entry doesn't exist, the entry with the earliest expires_at is evicted (LRU-style). Prevents unbounded growth of the neighbor cache under ARP flood attacks. Mirrors Linux /proc/sys/net/ipv4/neigh/default/gc_thresh3. netcfg exposes /scheme/netcfg/ifaces/eth0/arp/max → '1024' All 31 tests pass.