OPENTHREAD_CONFIG_DELAY_AWARE_QUEUE_MANAGEMENT_ENABLE macro

@def OPENTHREAD_CONFIG_DELAY_AWARE_QUEUE_MANAGEMENT_ENABLE Define to 1 to enable delay-aware queue management for the send queue. When enabled device will monitor time-in-queue of messages in the direct tx queue and if the wait time is lager than specified thresholds it may update ECN flag (if message indicates it is ECN-capable) or drop the message.