m_advance
l3hdr = m_advance(&m, &offset, m0->m_pkthdr.l2hlen);
m_advance(&m, &offset, m0->m_pkthdr.l2hlen);
eh = m_advance(&m, &offset, m0->m_pkthdr.l3hlen +
l3hdr = m_advance(&m, &offset, m0->m_pkthdr.inner_l2hlen);
m_advance(&m, &offset, m0->m_pkthdr.inner_l2hlen);
tcp = m_advance(&m, &offset, m0->m_pkthdr.inner_l3hlen);
tcp = m_advance(&m, &offset, m0->m_pkthdr.l3hlen);