nsclick: Correct offset when parsing serialized defines.

Hey,

i finally managed to do a fork of click on github. Now it should be a lot easier to provide patches for click.

This patch is required fixing a bug in parsing variable definitions from ns3. Without this patch, only the first variable is parsed correctly. I already sent you this patch on 25.04.2013 via the click mailing list, but it seems the patch didn't make it into master until now.