Be more conservative when computing maxmtu.
Be more conservative when computing maxmtu.

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