NETINFO cells are used for clock skew checks

In tor-spec.txt, this is outdated:

   Implementations MAY use the timestamp value to help decide if their
   clocks are skewed.  Initiators MAY use "other OR's address" to help
   learn which address their connections are originating from, if they do
   not know it.  [As of 0.2.3.1-alpha, nodes use neither of these values.]