fix altitude for telemetry, instead of using zero

src/helpers/sensors/LocationProvider.h

@@ -8,6 +8,7 @@ class LocationProvider {
 public:
     virtual long getLatitude() = 0;
     virtual long getLongitude() = 0;
+    virtual long getAltitude() = 0;
     virtual bool isValid() = 0;
     virtual long getTimestamp() = 0;
     virtual void reset();

src/helpers/sensors/MicroNMEALocationProvider.h

@@ -61,6 +61,11 @@ public :
 
     long getLatitude() override { return nmea.getLatitude(); }
     long getLongitude() override { return nmea.getLongitude(); }
+    long getAltitude() override { 
+        long alt = 0;
+        nmea.getAltitude(alt);
+        return alt;
+    }
     bool isValid() override { return nmea.isValid(); }
 
     long getTimestamp() override {