As the the SoC uses implicit vlan tagging for dual MAC support, the
offload feature breaks when using double tagging.
This is backport of 9da2b56760 from trunk.
As the layout of the files has changed a cherry-pick was not possible.
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: John Crispin <john@phrozen.org>
f4689c739b