Add omitted prototype for check_xroutes.
Add omitted prototype for check_xroutes.

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