net/mlx5: E-switch, When eswitch is unsupported, return -EOPNOTSUPP

When eswitch is unsupported, currently -EPERM error code is returned
instead of -EOPNOTSUPP.

Due to this VF device's devlink virtual port is not enumerated because
port_function_get() callback returned -EPERM instead of -EOPNOTSUPP.

Hence, return the error code -EOPNOTSUPP when eswitch is unsupported.

Fixes: bd939753 ("net/mlx5: E-switch, Introduce and use eswitch support check helper")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>