* Tunnels: Change the default variance from 1 to 0.

      Under the one-packet-enough theory, and the fact that most
      tunnels in a x+1 pool are of length x, variable lengths
      don't really help that much. Also, a default of 1 led
      to all sorts of problems with iMule/SAM, who was not
      setting the variance properties.
      This will affect exploratory tunnels for new users,
      and those that have never saved a change on configtunnels.jsp,
      and iMule users 1.4.5 and earlier.