With de510265 the explicit tagging of
the CPU port was removed. This leads to a not working default network
config, with vlans enabled but disabled CPU tagging, for boards where
all switch ports are having the same role.

In case the ports are having different roles set, tagging is is set
implicit for the CPU port by ucidef_add_switch().

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