Fix potential stack smash
Fix potential stack smash

When built with stack checking, snprintf fails,
even though we "know" port numbers can't be more
than 5 digits long.
cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond