Merge pull request #336 from pigrew/edpt_close

> If you notice my chain of events above, the bulk transfer was started BEFORE the SET_INTERFACE call. The USB device hardware swaps the order of them being delivered. On STM32, it gives priority to the lower-numbered EP index.

It shouldn't be a matter, control is 2+ stage, before sending the setup. Host should stop all communication to the endpoint that It wants to close.

src/device/dcd.h

@@ -123,6 +123,10 @@ void dcd_edpt0_status_complete(uint8_t rhport, tusb_control_request_t const * re
 // Configure endpoint's registers according to descriptor
 bool dcd_edpt_open        (uint8_t rhport, tusb_desc_endpoint_t const * p_endpoint_desc);
 
+// Close an endpoint.
+// Since it is weak, caller must TU_ASSERT this function's existence before calling it.
+void dcd_edpt_close        (uint8_t rhport, uint8_t ep_addr) TU_ATTR_WEAK;
+
 // Submit a transfer, When complete dcd_event_xfer_complete() is invoked to notify the stack
 bool dcd_edpt_xfer        (uint8_t rhport, uint8_t ep_addr, uint8_t * buffer, uint16_t total_bytes);