wcn36xx: Enable firmware link monitoring

This patch switches on CONNECTION_MONITOR. Once done it is up to the
firmware to send keep alive and to monitor the link state.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201103121735.291324-3-bryan.odonoghue@linaro.org