net/mlx4_en: Change Connect-X description in kconfig

The mlx4_en driver support also 1Gbit and 40Gbit Ethernet devices,
changed the driver description in the menuconfig to reflect that.

Signed-off-by: Eyal Perry <eyalpe@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>