QDISC: pfifo_fast reordering in tx for single_q device

Hi Guys,

Raised a bug already, just posting here for quicker response.
https://bugzilla.kernel.org/show_bug.cgi?id=206497

This has one fix for pfifo reorder, but still sometimes able to repro, esp with
multiple QoS streams.

Cheers.
Chaitanya.