net/mlx5: Disable eswitch as the first thing in mlx5_unload()

The eswitch disable call does removal of all representors. Do that
before clearing the SF device table and maintain the same flow as during
SF devlink port removal, where the representor is removed before
the actual SF is removed.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>