Rover: add support for 4th mavlink channel

APMrover2/Parameters.h

@@ -71,6 +71,7 @@ public:
         k_param_serial2_protocol,   // deprecated, can be deleted
         k_param_serial_manager,     // serial manager library
         k_param_cli_enabled,
+        k_param_gcs3,
 
         //
         // 130: Sensor parameters

APMrover2/Parameters.pde

@@ -455,6 +455,12 @@ const AP_Param::Info var_info[] PROGMEM = {
     GOBJECTN(gcs[2],  gcs2,       "SR2_",     GCS_MAVLINK),
 #endif
 
+#if MAVLINK_COMM_NUM_BUFFERS > 3
+    // @Group: SR3_
+    // @Path: GCS_Mavlink.pde
+    GOBJECTN(gcs[3],  gcs3,       "SR3_",     GCS_MAVLINK),
+#endif
+
     // @Group: SERIAL
     // @Path: ../libraries/AP_SerialManager/AP_SerialManager.cpp
     GOBJECT(serial_manager,         "SERIAL",   AP_SerialManager),

APMrover2/system.pde

@@ -118,6 +118,11 @@ static void init_ardupilot()
     gcs[2].setup_uart(serial_manager, AP_SerialManager::SerialProtocol_MAVLink, 1);
 #endif
 
+#if MAVLINK_COMM_NUM_BUFFERS > 3
+    // setup serial port for fourth telemetry port (not used by default)
+    gcs[3].setup_uart(serial_manager, AP_SerialManager::SerialProtocol_MAVLink, 2);
+#endif
+
     // setup frsky telemetry
 #if FRSKY_TELEM_ENABLED == ENABLED
     frsky_telemetry.init(serial_manager);