Iptables related fixes

  At hypervm start executing iptables -t nat -L causes hanging if
  the nat table is full with unresolvable ips. (With a table updated from
  DROP this could take several hours.)

  vpstraffic openvzlib handled iptables rules bad.
  There was no -j ACCEPT and it could not delete the rules at startup
  so it kept doubling them.
  Also added ip6tables support.