netmap: round robin fixes by tobias@
netmap: multithreading fixes

* If multiple threads poll individual devices, we'll run into
  trouble with a global private stash.  Now per-thread.

* The timestamp may jump back for reasons we haven't debugged
  yet.  To not let that effect the higher layer time accounting
  we'll have to ignore small backwards leaps coming from netmap(4).
li: small tweaks for DNS and categories
token: add reference counting and tighten tests
netmap: implement single-device recv() plus a typo fix