Don't repeatedly reinstall blackhole routes.
Don't repeatedly reinstall blackhole routes.

tcatm/babeld,boutier/babeld,Drooids/babeld,wlanslovenija/babeld,woniullb/babeld,Gwendocg/babeldToS,jech/babeld,dtaht/babeld-shortrtt-metrics,wlanslovenija/babeld,jech/babeld,sudomesh/babeld,Gwendocg/babeldToS