OPENTHREAD_CONFIG_MAC_COLLISION_AVOIDANCE_DELAY_ENABLE macro

@def OPENTHREAD_CONFIG_MAC_COLLISION_AVOIDANCE_DELAY_ENABLE Define as 1 to enable collision avoidance delay feature, which adds a delay wait time after a successful frame tx to a neighbor which is expected to forward the frame. This delay is applied before the next direct frame tx (towards any neighbor) on an FTD. The delay interval is specified by `OPENTHREAD_CONFIG_MAC_COLLISION_AVOIDANCE_DELAY_INTERVAL` (in milliseconds).