Fix computation of exponential decay in route_smoothed_metric.
Fix computation of exponential decay in route_smoothed_metric.

We're working with deltas, not with absolute values, so we need to
subtract 1.  Oh, and it's multiplication, not division.

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