Function ipv4_checksum

pub fn ipv4_checksum(
    data: &[u8],
    skipword: usize,
    extra_data: &[u8],
    source: &Ipv4Addr,
    destination: &Ipv4Addr,
    next_level_protocol: IpNextHeaderProtocol,
) -> u16be

Calculate the checksum for a packet built on IPv4. Used by UDP and TCP.