Function ipv4_is_usable_host 

pub const fn ipv4_is_usable_host(address: &[u8; 4]) -> bool

Whether an IPv4 address is a usable host address: unicast, and not link-local.

This is the definition IP_READY is stated in terms of. A self-assigned 169.254 address reaches only the link, exactly as fe80:: does, and a device that fell back to one is a device whose DHCP failed.