net: dsa: mv88e6xxx: set 802.1Q mode to Fallback

The current Secure port mode requires the port-based VLANs to also be
valid in the 802.1Q VLAN Table Unit. The current hardware bridging
support only configures the port-based VLANs, thus is broken.

A new patchset is required to adapt the hardware bridging code to fully
support the Secure port mode.

In the meantime, change the 802.1Q mode of every ports to Fallback,
which filtering is more permissive, and doesn't add this restriction to
handle port-based and tagged-based VLANs.

Fixes: 8efdda4a ("net: dsa: mv88e6xxx: use port 802.1Q mode Secure")
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>