Created attachment 2360 [details]
Suggested Patch

WifiMode::GetDataRate function seems to calculate the symbol rate for 20Mhz channel, while considers other differences between 20, 10, and 5 Mhz channels such as the number of usable subcarriers.
The function uses following line to calculate the symbol rate:
      double symbolRate = (1 / 4.0) * 1e6;
While is should be:
      double symbolRate = (1 / 8.0) * 1e6;
and:
      double symbolRate = (1 / 16.0) * 1e6;
for the 10 Mhz channel width and the 5 Mhz channel width, respectively.