wlcore: use new set bandwidth command to adjusting channel BW

We support changing the channel BW when we started the STA role on
a 40Mhz bandwidth. Otherwise a reconnection is required.
Save the started channel width and use it when channel width updates
arrive.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>