start to add msc host, fix dangerous problem with unstable device when plugged --> 200 ms delay. 50ms delay after each port reset

demos/host/src/keyboard_app.c

@@ -178,4 +178,13 @@ static inline uint8_t keycode_to_ascii(uint8_t modifier, uint8_t keycode)
     hid_keycode_to_ascii_tbl [modifier & (KEYBOARD_MODIFIER_LEFTSHIFT | KEYBOARD_MODIFIER_RIGHTSHIFT) ? 1 : 0] [keycode];
 }
 
+#else
+
+// dummy implementation to remove #ifdef in main.c
+void keyboard_app_init(void) { }
+OSAL_TASK_FUNCTION( keyboard_app_task ) (void* p_task_para)
+{
+  OSAL_TASK_LOOP_BEGIN
+  OSAL_TASK_LOOP_END
+}
 #endif