Add j1939 VP2 details

Add 3 missing unused bytes (for a message len of 8) to the j1939 VP2 struct, as well as range information for the existing parameters.

j1939_vehicle_position/j1939_vehicle_position_cmn.h

@@ -142,32 +142,35 @@ j1939_vp1_set_longitude(struct j1939_vp1_packet *packet, int32_t longitude)
 /**
  * struct j1939_vp2_packet - Represents the PGN 64502 Vehicle
  *                                         Position 2 packet
- * FIXME: current packet layout is guessed based on limited information:
- * https://www.isobus.net/isobus/pGNAndSPN/10801?type=PGN
  *
  * @total_satellites: Total number of satellites in view
  *           - SPN: 8128
  *           - Data Length: 1 byte
+ *           - Range: 0 to 250
  *
  * @hdop: Horizontal dilution of precision
  *           - SPN: 8129
  *           - Data Length: 1 byte
  *           - Resolution: 0.1
+ *           - Range: 0.0 to 25.0
  *
  * @vdop: Vertical dilution of precision
  *           - SPN: 8130
  *           - Data Length: 1 byte
  *           - Resolution: 0.1
+ *           - Range: 0.0 to 25.0
  *
  * @pdop: Position dilution of precision
  *           - SPN: 8131
  *           - Data Length: 1 byte
  *           - Resolution: 0.1
+ *           - Range: 0.0 to 25.0
  *
  * @tdop: Time dilution of precision
  *           - SPN: 8132
  *           - Data Length: 1 byte
  *           - Resolution: 0.1
+ *           - Range: 0.0 to 25.0
  *
  * This structure defines each component of the Vehicle Position 2 as described
  * in PGN 64502.
@@ -178,6 +181,9 @@ struct j1939_vp2_packet {
 	uint8_t vdop;             /* SPN 8130 */
 	uint8_t pdop;             /* SPN 8131 */
 	uint8_t tdop;             /* SPN 8132 */
+	uint8_t unused5;          /* Always 0xFF */
+	uint8_t unused6;          /* Always 0xFF */
+	uint8_t unused7;          /* Always 0xFF */
 } __attribute__((__packed__));
 
 /**