m_split
n->m_next = m_split(m, len, wait);
o = m_split(m, oobmark, wait);
if ((n = m_split(m, ipoff2, M_DONTWAIT)) == NULL)
n = m_split(m, len, M_NOWAIT);
if ((t = m_split(m, offset, M_DONTWAIT)) == NULL)
struct mbuf *m_split(struct mbuf *, int, int);