Patch for: T31622

When importing a 3ds file from yepsketch.com the imported object was coming out way too big. I wanted to play around with importing objects using a scripts and found out that bpy.ops.import_scene.autodesk_3ds took a constrain_size parameter... but it didn't seem to have any effect. While digging through the code I discovered that the processing of this parameter is completely disabled.

I've attached a patch to fix the issue and a sample .3ds file which is scaled incorrectly for testing is attached to the bug.