AP_NavEKF2: restrict setting of EKF origin

only allow EKF origin to be set if EKx_GPS_TYPE is set to 3, which is
used for indoor operation

libraries/AP_NavEKF2/AP_NavEKF2.cpp

@@ -1096,6 +1096,13 @@ bool NavEKF2::getOriginLLH(int8_t instance, struct Location &loc) const
 // Returns false if the filter has rejected the attempt to set the origin
 bool NavEKF2::setOriginLLH(const Location &loc)
 {
+    if (_fusionModeGPS != 3) {
+        // we don't allow setting of the EKF origin unless we are
+        // flying in non-GPS mode. This is to prevent accidental set
+        // of EKF origin with invalid position or height
+        gcs().send_text(MAV_SEVERITY_WARNING, "EKF2 refusing set origin");
+        return false;
+    }
     if (!core) {
         return false;
     }