net: dsa: move reset of VLAN filtering to dsa_port_switchdev_unsync_attrs

In dsa_port_switchdev_unsync_attrs() there is a comment that resetting
the VLAN filtering isn't done where it is expected. And since commit
108dc874 ("net: dsa: Avoid cross-chip syncing of VLAN filtering"),
there is no reason to handle this in switch.c either.

Therefore, move the logic to port.c, and adapt it slightly to the data
structures and naming conventions from there.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>