State table reorganisation
State linking


Inbound: we store a pointer to the stackside state key in the pkthdr

Outbound: finding the state key is as simple as:

  if (dir == PF_OUT && m->m_pkthdr.pf.statekey &&
    ((struct pf_state_key *)m->m_pkthdr.pf.statekey)->reverse)
      sk = ((struct pf_state_key *)m->m_pkthdr.pf.statekey)->reverse;

no more redundant state table searches!