void ctl_arp_set_cache_size(unsigned size);
ctl_arp_set_cache_size sets the maximum number of entries held in the ARP cache to size. ctl_arp_set_cache_size restricts the range of size to be between 4 and 256 entries.
ctl_arp_set_cache_size does not clear the ARP cache when it is resized, but if the cache is contracted, entries in the cache cache are discarded in reverse age order, from oldest to youngest.
ctl_arp_set_cache_size is thread-safe.