wlcore: update basic rates on channel switch

On channel switch we have to update the basic rates, in
order to reflect possible band changes (otherwise, we
might start beaconing on 11a with the default rates
of 11g).

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>