net/mlx5: Bridge, identify port by vport_num+esw_owner_vhca_id pair

Following patches in series allow traffic between vports of different
eswitch instances, which requires addressing bridge port by
vport_num+esw_owner_vhca_id pair since vport_num is only unique
per-eswitch. As a preparation, extend struct mlx5_esw_bridge_port with
'esw_owner_vhca_id' field and use it as part of key for
mlx5_esw_bridge->vports xarray.

With this change we can't rely on switchdev_handle_port_obj_add() helper to
get mlx5 representor from stacked device because we need specifically
representor from parent eswitch that registered the callback to obtain
correct esw_owner_vhca_id. The helper doesn't allow passing additional
parameters to predicate function and doesn't provide access to the notifier
block to obtain eswitch through br_offloads. Implement custom helpers to
obtain mlx5 representor and use them in
mlx5_esw_bridge_port_obj_{add|del|attr_set}() implementations.

Remove direct pointer to parent bridge from struct mlx5_vport as it is no
longer needed.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>