Use a opção chanlist
com ifconfig
;
chanlist channels
Set the desired channels to use when scanning for access points,
neighbors in an IBSS network, or looking for unoccupied channels
when operating as an access point. The set of channels is speci‐
fied as a comma-separated list with each element in the list rep‐
resenting either a single channel number or a range of the form
“a-b”. Channel numbers must be in the range 1 to 255 and be per‐
missible according to the operating characteristics of the
device.