Move accounting of fc->num_waiting to the point where the request actually
starts waiting.  This is earlier than the current queue_request() for
background requests, since they might be waiting on the fc->bg_queue before
being queued on fc->pending.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Reviewed-by: NAshish Samant <ashish.samant@oracle.com>