cpu_in_cksum
*csump = cpu_in_cksum(m, m->m_pkthdr.len - off, off, 0);
int cpu_in_cksum(struct mbuf*, int, int, uint32_t);
int cpu_in_cksum(struct mbuf *, int, int, uint32_t);
return cpu_in_cksum(m, len, off, sum);
return cpu_in_cksum(m, len, off, 0);
return cpu_in_cksum(m, len, 0, 0);
return cpu_in_cksum(m, len, off, sum);
return cpu_in_cksum(m, len, off, 0);
new_sum = cpu_in_cksum(m, len, off, init_sum);
(void)cpu_in_cksum(m, len, off, init_sum);
int cpu_in_cksum(struct mbuf*, int, int, uint32_t);