Function if_freenameindex 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn if_freenameindex(s: *mut if_nameindex)

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/if_freenameindex.html.

Safety

this is a no-op: the list returned by if_nameindex() is a ref to a constant