[lwip-users] using sockets interface

[A G]

Hi
When I use the sockets interface (lwip/sockets.h), what are lwip's sockets 
running over? Or is it determined by netif_init_fn when adding the netif in 
netif_add?

For example could I create a new netif type that runs over RAW linux sockets, 
and make lwip sockets run over that by passing in my new netif_init_fn?

Also is there a netif that runs over linux sockets? I see in the contrib 
projects, there is reference to a unixif, but based on what I have seen, this 
looks something specific to the examples only, is this correct?

Thanks