iwlwifi: mvm: don't send a CSA command the firmware doesn't know

We introduced a new flow to remove an on-going CSA but we
assumed the firwmare understands the
CHANNEL_SWITCH_TIME_EVENT_CMD. This is not true for 7265 and down.

Don't send this command for those devices, but rather use the older
command.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008181047.2574e3e47927.Ic0c56411da1096e9a45ee5c3383edf777c5baca0@changeid