AP_Beacon: allow hwdefs to override number of beacons

... also a few other variables.

Also move these out of the main header file as one is internal and the others should go in the ocnfig. in case the values are used elsewhere

libraries/AP_Beacon/AP_Beacon.cpp

@@ -28,6 +28,10 @@
 
 extern const AP_HAL::HAL &hal;
 
+#ifndef AP_BEACON_MINIMUM_FENCE_BEACONS
+#define AP_BEACON_MINIMUM_FENCE_BEACONS 3
+#endif
+
 // table of user settable parameters
 const AP_Param::GroupInfo AP_Beacon::var_info[] = {
 

libraries/AP_Beacon/AP_Beacon.h

@@ -25,10 +25,6 @@
 
 class AP_Beacon_Backend;
 
-#define AP_BEACON_MAX_BEACONS 4
-#define AP_BEACON_TIMEOUT_MS 300
-#define AP_BEACON_MINIMUM_FENCE_BEACONS 3
-
 class AP_Beacon
 {
 public:

libraries/AP_Beacon/AP_Beacon_config.h

@@ -6,6 +6,14 @@
 #define AP_BEACON_ENABLED 1
 #endif
 
+#ifndef AP_BEACON_MAX_BEACONS
+#define AP_BEACON_MAX_BEACONS 4
+#endif
+
+#ifndef AP_BEACON_TIMEOUT_MS
+#define AP_BEACON_TIMEOUT_MS 300
+#endif
+
 #ifndef AP_BEACON_BACKEND_DEFAULT_ENABLED
 #define AP_BEACON_BACKEND_DEFAULT_ENABLED AP_BEACON_ENABLED
 #endif