Copter: add support for 4th mavlink channel

ArduCopter/Parameters.h

@@ -193,6 +193,7 @@ public:
         k_param_ch11_option,
         k_param_ch12_option,     // 123
         k_param_takeoff_trigger_dz,
+        k_param_gcs3,            // 125
 
         //
         // 140: Sensor parameters

ArduCopter/Parameters.pde

@@ -884,6 +884,12 @@ 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: AHRS_
     // @Path: ../libraries/AP_AHRS/AP_AHRS.cpp
     GOBJECT(ahrs,                   "AHRS_",    AP_AHRS),

ArduCopter/system.pde

@@ -139,6 +139,11 @@ 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
+
 #if FRSKY_TELEM_ENABLED == ENABLED
     // setup frsky
     frsky_telemetry.init(serial_manager);