usbcore: track whether interfaces are suspended

Currently we rely on intf->dev.power.power_state.event for tracking
whether intf is suspended.  This is not a reliable technique because
that value is owned by the PM core, not by usbcore.  This patch (as718b)
adds a new flag so that we can accurately tell which interfaces are
suspended and which aren't.

At first one might think these flags aren't needed, since interfaces
will be suspended along with their devices.  It turns out there are a
couple of intermediate situations where that's not quite true, such as
while processing a remote-wakeup request.


Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>