e100: implemenet set_phys_id

Based on the original patch from Stephen Hemminger.
Implement set_phys_id to control LED.

CC: Stephen Hemminger <shemminger@vyatta.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>