Applicable to AU/BU with HW revision B and lower
(for units with HW revision C and higher replaced by
brzaccVLCurrentUOperatingFrequencyNew to support a resolution
of 0.5 MHz).
The operating frequency in MHz.
For 5.8GHz products with SW version below 2.0 the range is
5740 to 5830 MHz using 10MHz resolution.
For units with SW version 2.0 and up the range is as defined
in the selected Sub Band.