IPH_OFFSET
struct ip *ih = (struct ip *)(mtod(m, uint8_t *) + IPH_OFFSET);
struct ip *ih = (struct ip *)(mtod(sm, uint8_t *) + IPH_OFFSET);
struct ip *nih = (struct ip *)(mtod(m, uint8_t *) + IPH_OFFSET);
th = (struct tcphdr *)(mtod(sm, uint8_t *) + IPH_OFFSET + sizeof (struct ip));
DPRINTF("m_adj(%d)\n", (int)(IPH_OFFSET + tcpiphlen));
m_adj(m, IPH_OFFSET + tcpiphlen);
frag->page_offset + IPH_OFFSET + tcpiphlen;
struct ip *sih = (struct ip *)(mtod(m, uint8_t *) + IPH_OFFSET);