dns_name_getlabelsequence
dns_name_getlabelsequence(name, n, labels - n, &tname);
dns_name_getlabelsequence(name, 0, n, prefix);
dns_name_getlabelsequence(name, start, n, &tname);
dns_name_getlabelsequence(const dns_name_t *source, unsigned int first,
dns_name_getlabelsequence(name, l1 - l2, l2, target);
dns_name_getlabelsequence(name, 0, l1 - l2, target);