ctllen
offsetof(struct pkthdr, ctllen), "unix/dgram can not store ctllen");
f->m_pkthdr.ctllen = ctl;
so->so_rcv.uxdg_ctl += m->m_pkthdr.ctllen;
sb->uxdg_ctl -= m->m_pkthdr.ctllen;
so->so_rcv.sb_ctl -= m->m_pkthdr.ctllen;