ethtool: Extend the ethtool API to obtain plugin module eeprom data

ETHTOOL_GMODULEINFO returns a new struct ethtool_modinfo that will return the
type and size of plug-in module eeprom (such as SFP+) for parsing
by userland program.

ETHTOOL_GMODULEEEPROM returns the raw eeprom information
using the existing ethtool_eeprom structture to return the data

Signed-off-by: Stuart Hodgson <smhodgson@solarflare.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>