core: frontend: NMEA Injector should warn users when GPS is not configured as MAVLink

[ES-Alexander]

Current behaviour

Per this forum topic if the NMEA injector is set up without specifying a MAVLink GPS_TYPE in the autopilot parameters, the autopilot may not properly register the GPS input values, which can lead the user to think their GPS (or the NMEA injection) is not working properly.

Expected or desired behaviour

As @Williangalvani suggested in the forum thread, it would be good if the NMEA Injector page checks whether the connected autopilot has a GPS_TYPE parameter set to MAVLink, and provide a warning if that is not the case.

Prerequisites

• [X] I have checked to make sure that a similar request has not already been filed or fixed.