AP_SerialManager: fix includes place and order

libraries/AP_SerialManager/AP_SerialManager.cpp

@@ -21,6 +21,7 @@
  */
 
 #include <AP_HAL/AP_HAL.h>
+#include <AP_Math/AP_Math.h>
 #include "AP_SerialManager.h"
 
 extern const AP_HAL::HAL& hal;

libraries/AP_SerialManager/AP_SerialManager.h

@@ -21,10 +21,9 @@
  */
 #pragma once
 
-#include <AP_Math/AP_Math.h>
-#include <AP_Common/AP_Common.h>
 #include <AP_HAL/AP_HAL.h>
 #include <GCS_MAVLink/GCS_MAVLink.h>
+#include <AP_Param/AP_Param.h>
 
 // we have hal.uartA to hal.uartG
 #define SERIALMANAGER_NUM_PORTS 7