ath11k: Identify DFS channel when sending scan channel list command

WMI_CHAN_INFO_DFS flag should be set when configuring a DFS channel
included in scan channel list. Without it, firmware will not send a
probe request frame which is needed in connection to an AP configured
with hidden SSID/network_id. So fix this to allow probe request frames
to be sent in cases where a beacon frame has been seen on the channel
first.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1

Signed-off-by: Baochen Qiang <bqiang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211011054919.77071-1-bqiang@codeaurora.org