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

This reverts commit e9bf9694.

The topic of the reverted patch is the support for switches with global
VLAN filtering, added by commit 061f6a50 ("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 2cafa72e ("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 8841f6e6

 ("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>