net/mlx5: E-switch, Fix switchdev mode after devlink reload

The cited commit removes eswitch mode none. So after devlink reload
in switchdev mode, eswitch mode is not changed. But actually eswitch
is disabled during devlink reload.

Fix it by setting eswitch mode to legacy when disabling eswitch
which is called by reload_down.

Fixes: f019679e ("net/mlx5: E-switch, Remove dependency between sriov and eswitch mode")
Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>