Add route_metric accessor.
Add route_metric accessor.

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