first cleanup for 802.3 case

First cleanup for 

https://github.com/rapid7/metasploit-framework/pull/1408

I've used the test data available at:

http://packetlife.net/captures/802.1X.cap

I would need test data for the 802.11 case. Also captures with known passwords would be needed to verify the challenge resolving code. Can you help to provide pcaps for testing? Any chance to ask the original author?

Please review my fixes until the moment and land this pull request once you feel comfortable, so the original https://github.com/rapid7/metasploit-framework/pull/1408 will be updated automatically :)

Thanks in advance!

juan