Adding clarification to TN3270 Dissector

adding some comments and output information to make it clear that a z/OS TSO logon has been found as previously it was unclear what the username/password is for (it simply displayed the IP and found userid/password). 
Update to etter.conf to contain TN3270 dissector

The TN3270 protocol for mainframes runs on port 23 (cleartext) and port 992 (SSL Encrypted). This update is to add those two items to the current etter.conf. 
Merge pull request #81 from mainframed/master

Changes to TN3270 Dissector to clarify what it's getting and updates to ettercap.conf to add default z/OS TCP ports