net/mlx5: Introduce mlx5_eswitch_load/unload_sf_vport() and use it from SF code

Similar to the PF/VF helpers, introduce a set of load/unload helpers
for SF vports. From there, call mlx5_eswitch_load/unload_vport() which
are common for PFs/VFs and newly introduced SF helpers.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Shay Drory <shayd@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>