GSM IMSI Catcher Detection

For the detection of IMSI catchers (fake base stations) in GSM I am adding the following functionality to rayhunter:

• parsing of gsm packets into rust structs
• network traffic analyzers utilizing these indicators:
• cell reselection and hysteresis parameters
• ciphering mode
• identity requests

I needed to read a lot of specifications for this project. 3GPP does not publish them in a nice format, so I wrote the small script 3gpp-spec-downloader.