Thanks for the contribution! Since there is little output here (just distinguishing protocol versions), I feel that this would fit better as a UDP payload in the nmap-payloads file. I've already pushed a change to do this initially, and I'll update it to send both GTP v1 and v2 probes once we have multiple payload support (pending #1859). I've given you credit in the changelog, since it's your work that came up with the probes.