ixgb: convert to set_phys_id

Based on the original patch sent by Stephen Hemminger.

This version incorporates the ethtool changes that Bruce Allan
submitted.

CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Evan Swanson <evan.swanson@intel.com>