Protect against omitted being too large in network_prefix.
Protect against omitted being too large in network_prefix.

Thanks to Stephen Fisher.

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