net: dsa: b53: Let DSA call .port_vlan_filtering only when necessary

Since DSA has recently learned to treat better with drivers that set
vlan_filtering_is_global, doing this is no longer required.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>