net/mlx5: Fix LAG requirement when CONFIG_MLX5_ESWITCH is off

If CONFIG_MLX5_ESWITCH is not defined, test for SR-IOV being disabled,
instead of calling e-switch LAG prereq routine.

Since LAG with SRIOV is allowed only when switchdev mode is on.

Fixes: eff849b2 ("net/mlx5: Allow/disallow LAG according to pre-req only")
Signed-off-by: Aviv Heller <avivh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>