net: dsa: sja1105: add a new best_effort_vlan_filtering devlink parameter

This devlink parameter enables the handling of DSA tags when enslaved to
a bridge with vlan_filtering=1. There are very good reasons to want
this, but there are also very good reasons for not enabling it by
default. So a devlink param named best_effort_vlan_filtering, currently
driver-specific and exported only by sja1105, is used to configure this.

In practice, this is perhaps the way that most users are going to use
the switch in. It assumes that no more than 7 VLANs are needed per port.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>