Add warning about some errors possibly going unreported

Setting state to USB_TYPE_IDLE allows the library to recover from an error after the channels
have been cleared. But this might lead to some errors going unreported, and should be improved
in the future - but at least the library passes all our tests from higher levels in the stack
at this point, which it didn't before. Our tests don't show any signs of data loss when the
error recovery kicks in with the current solution. Fixing this last problem will probably take
quite some effort (time), which isn't possible at the moment.

Author: Alrik Vidstrom

src/targets/TARGET_STM/USBEndpoint_STM.cpp

@@ -153,6 +153,10 @@ void USBEndpoint::setState(USB_TYPE st)
         USBx_HC(hced->ch_num)->HCCHAR &= ~USB_OTG_HCCHAR_CHDIS;
         USBx_HC(hced->ch_num)->HCCHAR |= USB_OTG_HCCHAR_CHENA;
         // <--
+        // Set state to USB_TYPE_IDLE to allow the library to recover from the error.
+        // WARNING: This might lead to some errors going unreported, and should be improved in the future, but
+        //          at least the library passes all our tests from higher levels at this point, which it didn't
+        //          do before.
         state = USB_TYPE_IDLE;
     }
 }