[Module: NTRIP] Add config option for NEMA GGA Message

[mjohenneken]

based on this: https://discuss.ardupilot.org/t/mavproxy-ntrip-client-disconnects-when-second-client-joins-caster/139071/4

Allow to configure if the NMEA GPS messages is sent to Base Station (only required for VRS in RTK Networks) and can cause issues with certain NTRIP servers