lantiq: fix broadcasts and vlans in two iface mode

lantiq: fix broadcasts and vlans in two iface mode

The two phy operation mode where one phy is assigned to an interface
without lantiq,* device tree property and the other phy is assigned to
an interface with the lantiq,wan device property was broken with the
multicast package leaks between vlans fixes.

Move the multicast packages relevant portmap settings to the condition
which handles multicast packages for better readability.

Replace the priv->port_map based port_map only for the interface which
has the lantiq,switch device tree property set, to allow tagged
multicast packages in two phy mode where the lantiq,switch device tree
property isn't used.

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