Increase serial rx buffer size for USB communication

Marlin/Configuration_adv.h

@@ -1772,12 +1772,12 @@
 // Without XON/XOFF flow control (see SERIAL_XON_XOFF below) 32 bytes should be enough.
 // To use flow control, set this buffer size to at least 1024 bytes.
 // :[0, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048]
-#define RX_BUFFER_SIZE 256
+#define RX_BUFFER_SIZE 512
 
 #if RX_BUFFER_SIZE >= 1024
   // Enable to have the controller send XON/XOFF control characters to
   // the host to signal the RX buffer is becoming full.
-  //#define SERIAL_XON_XOFF
+  #define SERIAL_XON_XOFF
 #endif
 
 // Add M575 G-code to change the baud rate