net/mlx5e: Don't support phys switch id if not in switchdev mode

Support for phys switch id ndo added for representors and if
we do not have representors there is no need to support it.
Since each port return different switch id supporting this
block support for creating bond over PFs and attaching to bridge
in legacy mode.

This bug doesn't exist upstream as the code got refactored and the
netdev api is totally different.

Fixes: cb67b832 ("net/mlx5e: Introduce SRIOV VF representors")
Signed-off-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>