I have ported lwip to my device . I already have a linux kernel and the TCP/IP stack and the network driver on my device. I am going to replace the tcp/ip with this lwip stack .
Now ethernetif.c file is the lwip specific network interface driver file . May be what I can do is just use the eth0 created by the network device driver module in my lwip ethernet file and use the eth0 to send and receive the network packets.