Revert "net: dsa: sja1105: Clear VLAN filtering offload netdev feature"

This reverts commit e9bf969.

The topic of the reverted patch is the support for switches with global
VLAN filtering, added by commit 061f6a5 ("net: dsa: Add
ndo_vlan_rx_{add, kill}_vid implementation"). Be there a switch with 4
ports swp0 -> swp3, and the following setup:

ip link add br0 type bridge vlan_filtering 1
ip link set swp0 master br0
ip link set swp1 master br0

What would happen with VLAN-tagged traffic received on standalone ports
swp2 and swp3? Well, it would get dropped, were it not for the
.ndo_vlan_rx_add_vid and .ndo_vlan_rx_kill_vid implementations (called
from vlan_vid_add and vlan_vid_del respectively). Basically, for DSA
switches where VLAN filtering is a global attribute, we enforce the
standalone ports to have 'rx-vlan-filter: off [fixed]' in their ethtool
features, which lets the user know that all VLAN-tagged packets that are
not explicitly added in the RX filtering list are dropped.

As for the sja1105 driver, at the time of the reverted patch, it was
operating in a pretty handicapped mode when it had ports under a bridge
with vlan_filtering=1. Specifically, it was unable to terminate traffic
through the CPU port (for further explanation see "Traffic support" in
Documentation/networking/dsa/sja1105.rst).

However, since then, the sja1105 driver has made considerable progress,
and that limitation is no longer as severe now. Specifically, since
commit 2cafa72 ("net: dsa: sja1105: add a new
best_effort_vlan_filtering devlink parameter"), the driver is able to
perform CPU termination even when some ports are under bridges with
vlan_filtering=1. Then, since commit 8841f6e ("net: dsa: sja1105:
make devlink property best_effort_vlan_filtering true by default"), this
even became the default operating mode.

So we can now take advantage of the logic in the DSA core.

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

drivers/net/dsa/sja1105/sja1105_main.c

@@ -3049,21 +3049,6 @@ static void sja1105_teardown(struct dsa_switch *ds)
 	}
 }
 
-static int sja1105_port_enable(struct dsa_switch *ds, int port,
-			       struct phy_device *phy)
-{
-	struct net_device *slave;
-
-	if (!dsa_is_user_port(ds, port))
-		return 0;
-
-	slave = dsa_to_port(ds, port)->slave;
-
-	slave->features &= ~NETIF_F_HW_VLAN_CTAG_FILTER;
-
-	return 0;
-}
-
 static void sja1105_port_disable(struct dsa_switch *ds, int port)
 {
 	struct sja1105_private *priv = ds->priv;
@@ -3491,7 +3476,6 @@ static const struct dsa_switch_ops sja1105_switch_ops = {
 	.get_ethtool_stats	= sja1105_get_ethtool_stats,
 	.get_sset_count		= sja1105_get_sset_count,
 	.get_ts_info		= sja1105_get_ts_info,
-	.port_enable		= sja1105_port_enable,
 	.port_disable		= sja1105_port_disable,
 	.port_fdb_dump		= sja1105_fdb_dump,
 	.port_fdb_add		= sja1105_fdb_add,