ixgbe: Change Direct Attach Twinax cable detection for SFP+ NICs

The SFF specification for Direct Attach cable detection has now been
ratified.  Previously, DA cable detect was looking at the Twinaxial bit in
byte 9 of the SFP+ EEPROM.  The spec now defines active and passive DA
cables in byte 8 of the SFP+ EEPROM.  This patch changes the cable
detection for both 82598 and 82599 SFP+ adapters to conform to the new
spec.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>