[FL-1922] BLE buffer overflow (#789)

* rpc: increase RPC buffer size. Add get available buffer size API
* bt: add flow control characteristic to serial service
* ble: change updating flow control characteristic logic
* rpc: add buffer is empty callback
* bt: add notification about empty RPC buffer
* ble: add more debug info
* serial_service: add mutex guarding available buffer size
* ble: remove debug logs in serial service

core/furi/common_defines.h

@@ -64,4 +64,10 @@
 
 #ifndef TOSTRING
 #define TOSTRING(x) STRINGIFY(x)
+#endif
+
+#ifndef REVERSE_BYTES_U32
+#define REVERSE_BYTES_U32(x)                                                        \
+    ((((x)&0x000000FF) << 24) | (((x)&0x0000FF00) << 8) | (((x)&0x00FF0000) >> 8) | \
+     (((x)&0xFF000000) >> 24))
 #endif