The xemac_add() function provides a unified interface to add any AMD EMAC IP as
well as GigE core.
This function is a wrapper around the lwIP netif_add function that initializes the network
interface netif given its IP address ipaddr, netmask, the IP address of the
gateway, gw, the 6 byte ethernet address mac_ethernet_address, and the base address,
mac_baseaddr, of the axi_ethernetlite or axi_ethernet MAC core.
Prototype
struct netif *xemac_add(struct netif *netif, ip_addr_t *ipaddr, ip_addr_t *netmask, ip_addr_t *gw, unsigned char *mac_ethernet_address, unsigned mac_baseaddr)