net/mlx5: Disable reload while removing the device

While unregistration is in progress, user might be reloading the
interface.
This can race with unregistration in below flow which uses the
resources which are getting disabled by reload flow.

Hence, disable the devlink reloading first when removing the device.

     CPU0                                   CPU1
     ----                                   ----
local_pci_remove()                  devlink_mutex
  remove_one()                       devlink_nl_cmd_reload()
    mlx5_unregister_device()           devlink_reload()
                                       ops->reload_down()
                                         mlx5_unload_one()

Fixes: 4383cfcc

 ("net/mlx5: Add devlink reload")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>