net/mlx5: E-Switch, Return the correct devlink e-switch mode

Since mlx5 has also the NONE e-switch mode, we must translate from mlx5
mode to devlink mode on the devlink eswitch mode get call, do that.

While here, remove the mlx5_ prefix from the static function helpers
that deal with the mode to comply with the rest of the code.

Fixes: c930a3ad ('net/mlx5e: Add devlink based SRIOV mode change')
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>