[lwip-users] netif->hwaddr_len of loopback interface is not ETH_HWADDR_LEN

[Laurenz Altenmüller]

Hi,

I want to unit test some embedded firmware on native host arch by 
building it against the lwip unix port (latest master). Right now I want 
to add a fake IP and MAC to the ARP table with 
`etharp_add_static_entry()` so that the tested function can find it when 
it uses `etharp_query()` and then `etharp_find_addr()` in its 
implementation. For all this I'm using the netif I get from 
`netif_get_loopif()`.

Unfortunately I hit the assert in etharp.c:1139 ("netif->hwaddr_len must 
be the same as ETH_HWADDR_LEN for etharp!"). Using the debugger I can 
confirm that `netif->hwaddr_len` of my loopback netif is 0.

Should I even be able to use the loopback interface for ARP things? Am I 
just missing some initialization? (In my test's `setUp()` I call 
`sys_init(); mem_init(); netif_init(); test_netif=netif_get_loopif();`)

Cheers
Laurenz