net/mlx5e: Don't clear the whole vf config when switching modes

There is no need to reset all vf config (except link state) between
legacy and switchdev modes changes.
Also, set link state to AUTO, when legacy enabled.

Fixes: 3b83b6c2 ("net/mlx5e: Clear VF config when switching modes")
Signed-off-by: Dmytro Linkin <dmitrolin@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>