Fix seqno_compare and minus.
Fix seqno_compare and minus.

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