Skip CAC if the driver switches channel to non-DFS

Skip CAC if the driver switches channel to non-DFS

If an AP is started on a DFS channel (or any channels within its
bandwidth require DFS) and DFS is offloaded to the driver, hostapd needs
to wait for CAC to complete. But the driver may not do CAC and just
switches to a non-DFS channel instead. This would result in a failure to
start the AP because hostapd fails to receive a CAC complete event and
cannot finish interface setup.

Skip CAC and complete AP setup in the channel switch event handler for
this case.

Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>