nm_os_csum_raw
return nm_os_csum_fold(nm_os_csum_raw((uint8_t*)iph, sizeof(struct nm_iphdr), 0));
*check = nm_os_csum_fold(nm_os_csum_raw(data, datalen, 0));
*check = nm_os_csum_fold(nm_os_csum_raw(data, datalen, 0));
rawsum_t nm_os_csum_raw(uint8_t *data, size_t len, rawsum_t cur_sum);
csum = nm_os_csum_raw(src + vh->csum_start,
csum = nm_os_csum_raw(src, src_len, csum);