AP_BoardConfig: Increase the number of digits in the board serial number

Co-authored-by: Joshua Henderson <hendjoshsr71@gmail.com>

libraries/AP_BoardConfig/AP_BoardConfig.cpp

@@ -169,7 +169,7 @@ const AP_Param::GroupInfo AP_BoardConfig::var_info[] = {
     // @Param: SERIAL_NUM
     // @DisplayName: User-defined serial number
     // @Description: User-defined serial number of this vehicle, it can be any arbitrary number you want and has no effect on the autopilot
-    // @Range: -32768 32767
+    // @Range: -8388608 8388607
     // @User: Standard
     AP_GROUPINFO("SERIAL_NUM", 5, AP_BoardConfig, vehicleSerialNumber, 0),
 
@@ -337,6 +337,9 @@ const AP_Param::GroupInfo AP_BoardConfig::var_info[] = {
 
 void AP_BoardConfig::init()
 {
+    // PARAMETER_CONVERSION - Added: APR-2022
+    vehicleSerialNumber.convert_parameter_width(AP_PARAM_INT16);
+
     board_setup();
 
     AP::rtc().set_utc_usec(hal.util->get_hw_rtc(), AP_RTC::SOURCE_HW);

libraries/AP_BoardConfig/AP_BoardConfig.h

@@ -227,7 +227,7 @@ public:
 private:
     static AP_BoardConfig *_singleton;
     
-    AP_Int16 vehicleSerialNumber;
+    AP_Int32 vehicleSerialNumber;
 
     struct {
         AP_Int8 safety_enable;