net: dsa: move VLAN filtering setter

Move the DSA port code which sets VLAN filtering on a port in port.c,
where it belongs.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>