ramips: Allow to receive vlan over untag ports on MT7530

ramips: Allow to receive vlan over untag ports on MT7530

The MT7530 switch driver with enable_vlan set will automatically set all
ports to the user port mode. The hardware will remove the incoming vlan tag
on these ports and use it for its internal vlan. This is usually not wanted
and makes it impossible to communicate via vlan over the switch in both
directions.

It is possible to configure a switch port to "transparent mode" when this
port is only used as untag in the switch VLANs. This will disable the VLAN
untagging of packets when they were received on this port. The tagging on
"tag" ports based on the vlan id is still working.

The transparent port mode cannot be used when a port is both used in a VLAN
as "tag" and in another one as "untag" port.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47114 3c298f89-4303-0410-b956-a3cf2f4a3e73