OPENTHREAD_CONFIG_BORDER_ROUTING_ROUTER_ACTIVE_CHECK_TIMEOUT macro

@def OPENTHREAD_CONFIG_BORDER_ROUTING_ROUTER_ACTIVE_CHECK_TIMEOUT Specifies the timeout in msec for a discovered router on infra link side. This parameter is related to mechanism to check that a discovered router is still active. After this timeout elapses since the last received message (a Router or Neighbor Advertisement) from the router, routing manager will start sending Neighbor Solidification (NS) probes to the router to check that it is still active. This parameter can be considered to large value to practically disable this behavior.