ramips: fix edimax 6200nl switch config

With 3a9752bb and later changes to
ramips_set_preinit_iface() the default vlan config applied during
preinit was changed. These changes were made without updating the
default network config to ensure that vlan interfaces used for lan/wan
are still configured.

Fix the issue by using the default all LAN portmap and disabling not
connected switch ports using portdisable device tree parameter.

Signed-off-by: Mathias Kresin <dev@kresin.me>