network - Completely revamp the netisr / dispatch code

network - Completely revamp the netisr / dispatch code

* All netisrs are dispatched MPSAFE (followup in later commits)

* Centralize the protocol threads.  There is now just one thread
  per cpu managed by the netisr code.  No more separate tcp/udp threads
  on each cpu.

* Make the mbuf M_HASH/m_pkthdr.hash mechanic the central routing
  mechanic for netmsgs.

* Remove the netisr ip_mport and pktinfo_portfn stuff and replace with a
  cpufn function which handles M_HASH/m_pkthdr.hash when M_HASH is not
  already set.

* Seriously clean up the packet input paths.  Adjust ether_input_chain() and
  friends to not have to adjust the mbuf forwards and backwards, instead
  pass a header offset to the ni_cpufn function.  The ip pullup and other
  related code will use the offset to determine where the ip header is
  within the packet.