Drivers that support bridge offload need to be notified about changes to
the bridge's VLAN protocol so that they could react accordingly and
potentially veto the change.

Add a new switchdev attribute to communicate the change to drivers.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>