[BT] Enable to define MinimumRSSI from a macro in ini files (#1977)

main/config_BT.h

@@ -64,7 +64,9 @@ extern String stateBTMeasures(bool);
 #  define BLE_FILTER_CONNECTABLE 0 // Sets whether to filter publishing of scanned devices that require a connection.
 #endif // Setting this to 1 prevents overwriting the publication of the device connection data with the advertised data (Recommended for use with OpenHAB).
 
-#define MinimumRSSI -100 //default minimum rssi value, all the devices below -100 will not be reported
+#ifndef MinimumRSSI
+#  define MinimumRSSI -100 //default minimum rssi value, all the devices below -100 will not be reported
+#endif
 
 #ifndef Scan_duration
 #  define Scan_duration 10000 //define the duration for a scan; in milliseconds