net/mlx5: Prevent flow steering mode changes in switchdev mode

Changing flow steering modes is not allowed when eswitch is in switchdev
mode. This fix ensures that any steering mode change, including to
firmware steering, is correctly blocked while eswitch mode is switchdev.

Fixes: e890acd5 ("net/mlx5: Add devlink flow_steering_mode parameter")
Signed-off-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Link: https://patch.msgid.link/20250825143435.598584-9-mbloch@nvidia.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>