Because not all OSes will support the same set of serial port

options, here's a slight change to the API of ser_setup_config_box()
to make it filter its parity and flow control options using
platform-supplied bit masks.

[originally from svn r6820]

windows/wincfg.c

@@ -375,5 +375,5 @@ void win_setup_config_box(struct controlbox *b, HWND *hwndp, int has_help,
     /*
      * Serial back end is available on Windows.
      */
-    ser_setup_config_box(b, midsession);
+    ser_setup_config_box(b, midsession, 0x1F, 0x0F);
 }