AP_GPS: Read the vdop information from a ublox GPS

libraries/AP_GPS/AP_GPS.h

@@ -131,6 +131,7 @@ public:
         float ground_speed;                 ///< ground speed in m/sec
         int32_t ground_course_cd;           ///< ground course in 100ths of a degree
         uint16_t hdop;                      ///< horizontal dilution of precision in cm
+        uint16_t vdop;                      ///< vertical dilution of precision in cm
         uint8_t num_sats;                   ///< Number of visible satelites        
         Vector3f velocity;                  ///< 3D velocitiy in m/s, in NED format
         float speed_accuracy;

libraries/AP_GPS/AP_GPS_UBLOX.cpp

@@ -582,8 +582,10 @@ AP_GPS_UBLOX::_parse_gps(void)
         Debug("MSG_DOP");
         noReceivedHdop = false;
         state.hdop        = _buffer.dop.hDOP;
+        state.vdop        = _buffer.dop.vDOP;
 #if UBLOX_FAKE_3DLOCK
         state.hdop = 130;
+        state.hdop = 170;
 #endif
         break;
     case MSG_SOL: