mlx4_en: Added "set_ringparam" Ethtool interface implementation

Now using Ethtool to determine ring sizes, removed the module parameters
that controlled those values.
Modifying ring size requires restart of the interface.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>