switch_channel computed the CSA bandwidth as 40 << oper_chwidth, which
mismaps oper_chwidth 3 (80+80, must be 80 MHz plus center_freq2) to 320
and 9 (320 MHz) to 20480. Map the operating channel width to the actual
MHz bandwidth explicitly.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
b92df1e8da