Adjust the SNR when comparing BSSes based on Tx power config

Adjust the SNR when comparing BSSes based on Tx power config

The max transmit power of Standard Power (SP) Access Points (AP) on
6 GHz band and APs on 2.4 GHz and 5 GHz bands is limited by effective
isotropic radiated power (EIRP), while the max transmit power of Low
Power Indoor (LPI) APs on 6 GHz Band is limited by power spectral
density (PSD). Therefore the max transmit power of LPI APs grows as the
channel width increases, similar to the noise power which has constant
PSD.

Adjust the SNR of BSSes based on the transmit power config and max
channel width. EIRP limited APs usually have constant max transmit power
on different channel widths, their SNR decreases on larger channel width
because the noise power is higher, while PSD limited APs have constant
SNR over all channel widths.

Signed-off-by: Kaidong Wang <kaidong@chromium.org>