mt76: fix monitor rx FCS error in DFS channel

When setup monitor mode in DFS channel, mt76 send CH_SWITCH_DFS to
fw for channel config. This would cause rx performance bad while
monitoring frames. Settings CH_SWITCH_NORMAL in monitor mode would
get the same performance as normal channels.

Reviewed-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>