USB STORAGE DRIVER DELAYS

```
Description: There is a workaround for a bug in drivers/usbdev/usbdev_storage.c.
that involves delays. This needs to be redesigned to eliminate these
delays. See logic conditioned on CONFIG_USBMSC_RACEWAR.

If queuing of stall requests is supported by the DCD then this workaround
is not required. In this case, (1) the stall is not sent until all
write requests preceding the stall request are sent, (2) the stall is
sent, and then after the stall is cleared, (3) all write requests
queued after the stall are sent.

See, for example, the queuing of pending stall requests in the SAM3/4
UDP driver at arch/arm/src/sam34/sam_udp.c. There the logic is do this
is implemented with a normal request queue, a pending request queue, a
stall flag and a stall pending flag:

1) If the normal request queue is not empty when the STALL request is
received, the stall pending flag is set.
2) If addition write requests are received while the stall pending flag
is set (or while waiting for the stall to be sent), those write requests
go into the pending queue.
3) When the normal request queue empties successful and all of the write
transfers complete, the STALL is sent. The stall pending flag is
cleared and the stall flag is set. Now the endpoint is really stalled.
4) After the STALL is cleared (via the Clear Feature SETUP), the pending
request queue is copied to the normal request queue, the stall flag is
cleared, and normal write request processing resumes.

Status: Open
Priority: Medium
```