improve performance, use map instead of array traverse

[qiaosonghz]

pass test

[jpterry]

Hey @qiaosonghz,

I don't claim any original ownership or rights over this code. The source is originally from here: http://sourceforge.net/projects/pcapsipdump/. I mirrored it here because I needed it in a place I could use git instead of subversion. Additionally, I've moved on from the position where I had an interest in maintaining or supporting this repo. All that being said, I'm happy to accept this request, I just wanted to point you towards the original source incase you wanted to send the patch their way.