Fix reporting the MTU in spinfo_mtu for AF_CONN sockets.
Fix reporting the MTU in spinfo_mtu for AF_CONN sockets.

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