rt2x00usb: fix rx queue hang

Since commit ed194d13 ("usb: core: remove local_irq_save() around
 ->complete() handler") the handler rt2x00usb_interrupt_rxdone() is
not running with interrupts disabled anymore. So this completion handler
is not guaranteed to run completely before workqueue processing starts
for the same queue entry.
Be sure to set all other flags in the entry correctly before marking
this entry ready for workqueue processing. This way we cannot miss error
conditions that need to be signalled from the completion handler to the
worker thread.
Note that rt2x00usb_work_rxdone() processes all available entries, not
only such for which queue_work() was called.

This patch is similar to what commit df71c9cf ("rt2x00: fix order
of entry flags modification") did for TX processing.

This fixes a regression on a RT5370 based wifi stick in AP mode, which
suddenly stopped data transmission after some period of heavy load. Also
stopping the hanging hostapd resulted in the error message "ieee80211
phy0: rt2x00queue_flush_queue: Warning - Queue 14 failed to flush".
Other operation modes are probably affected as well, this just was
the used testcase.

Fixes: ed194d13 ("usb: core: remove local_irq_save() around ->complete() handler")
Cc: stable@vger.kernel.org # 4.20+
Signed-off-by: Soeren Moch <smoch@web.de>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>