Fix a integer overflow reported by Felix Weinrank.
Fix a integer overflow reported by Felix Weinrank.

JlnWntr/usrsctp,JlnWntr/usrsctp,sctplab/usrsctp,sctplab/usrsctp,faithfracture/usrsctp,weinrank/usrsctp,sctplab/usrsctp,CoolmanCZ/usrsctp,CoolmanCZ/usrsctp,weinrank/usrsctp,JlnWntr/usrsctp,CoolmanCZ/usrsctp,CoolmanCZ/usrsctp,faithfracture/usrsctp,faithfracture/usrsctp,weinrank/usrsctp