USB: more autosuspend timer stuff

This patch (as879) ties up some loose ends from an earlier patch.
These are things I didn't think to include at the time but which
clearly belonged there.

	If an autosuspend fails because driver activity races with
	the autosuspend call, restart the autosuspend timer.

	When a device is resumed by an external request, it counts
	as device activity and should update the last_busy time so
	that the next autoresume won't occur immediately.

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