unsigned ctl_arp_get_entry(CTL_NET_MAC_ADDR_t *dst, CTL_NET_IPv4_ADDR_t ip_addr);
ctl_arp_get_entry queries the ARP cache for the MAC address corresponding to the IP address ip_addr.
If the IP address is found in the ARP cache, the found MAC address is copied into the MAC address pointed to by mac_addr and a non-zero result is returned.
If the IP address is not found in the ARP cache, the MAC address pointed to by mac_addr is zeroed and ctl_arp_get_entry returns zero.
mac_addr can be null to query the presence of an IP-to-MAC mapping without returning the MAC address of the entry.
ctl_arp_get_entry only queries the cache and does not send an ARP request top the network if the IP address is not found in the cache.