USB: EHCI: warn on unexpectedly active QH

This patch adds a new warning message to ehci-hcd.  The warning is
triggered whenever the driver finds that the hardware has set the
Active bit in a QH at a time when the driver expects the QH to be
completely idle.  Such bugs have been observed by users in the past,
and since they can lead to serious problems (such as inability to
unlink an URB that never completes), it would be good to know about
them when they occur.

This won't fix these bugs; that's a bigger job for a later patch.  But
success isn't guaranteed, since this depends on aspects of the
hardware which are not documented in the EHCI spec or for which the
spec's recommendations are clearly unworkable.  It therefore seems
worthwhile to check for these bugs proactively.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Michael Reutman <mreutman@epiqsolutions.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>