bnx2x: cosmetics: Using ethtool_cmd_speed() API

This updates bnx2x to use the ethtool_cmd_speed() family of functions
(see b11f8d8c

 in 2.6.27-rc3 aka. "ethtool: Expand ethtool_cmd.speed to
32 bits") to get and set the link speed via ethtool. This allows to
avoid manually accessing ethtool_cmd's speed_hi field.

Signed-off-by: David Decotigny <decot@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>