drivers: net: cpsw: Add default vlan for dual emac case also

Dual EMAC works with VLAN segregation of the ports, so default vlan needs
to be added in dual EMAC case else default vlan will be tagged for all
egress packets and vlan unaware switches/servers will drop packets
from the EVM.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>