Address Resolution Protocol module for IP over Ethernet.
Functionally, ARP is divided into two parts. The first maps an IP address to a physical address when sending a packet, and the second part answers requests from other machines for our physical address.
This implementation complies with RFC 826 (Ethernet ARP). It supports Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6 if an interface calls etharp_gratuitous(our_netif) upon address change.
#include "lwip/opt.h"