[PATCH] realtek: fix RTL838x receive tag decoding

[Sander Vanheule]

On Thu, 2022-09-08 at 19:35 +0200, Bjørn Mork wrote:
> Commit dc9cc0d3e2a1 ("realtek: add QoS and rate control") replaced a
> 16 bit reserved field in the RTL83xx packet header with the initial
> cpu_tag word, shifting the real cpu_tag fields by one.  Adjusting for
> this new shift was partially forgotten in the new RX tag decoders.
> 
> This caused the switch to block IGMP, effectively blocking IPv4
> multicast.
> 
> The bug was partially fixed by commit 9d847244d9fd ("realtek: fix
> RTL839X receive tag decoding")
> 
> Fix on RTL838x too, including correct NIC_RX_REASON_SPECIAL_TRAP value.
> 
> Based-on-fix-by: Jan Hoffmann <jan at 3e8.eu>
> Fixes: dc9cc0d3e2a1 ("realtek: add QoS and rate control")
> Signed-off-by: Bjørn Mork <bjorn at mork.no>

I've cherry picked this patch for 22.03 too, so stable releases will also
benefit from this fix.

Best,
Sander