[routing-manager] fix BR can't send RA in the first 3 seconds (#7489)
[routing-manager] fix BR can't send RA in the first 3 seconds (#7489)


abtink/openthread,abtink/openthread,openthread/openthread,srickardti/openthread,srickardti/openthread,openthread/openthread,jwhui/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,jwhui/openthread,jwhui/openthread,openthread/openthread,srickardti/openthread,srickardti/openthread,abtink/openthread