MFC r265876:
  In cf_get_method, when we don't already know what clock speed the CPU is
  running at, guess the nearest value instead of looking for a value within
  25 MHz of the observed frequency.

  Prior to this change, if a system booted with Intel Turbo Boost enabled,
  the dev.cpu.0.freq sysctl is nonfunctional, since the ACPI-reported
  frequency for Turbo Boost states does not match the actual clock frequency
  (and thus no levels are within 25 MHz of the observed frequency) and the
  current performance level is read before a new level is set.

Relnotes:       Bug fix in power management on CPUs with Intel Turbo Boost