drivers: wifi: nrf700x: Ignore all failures in iface down

In case RPU is stuck and need a recovery, the failures in interface down
should be ignored as they are expected and we should proceed with device
removal that in turn removes power to the RPU.

TODO: This works for single VIF, but needs more thought for multi-VIF.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>