igb: Store the MAC address in the name in the PTP struct.

Change the name of the adapter in the PTP struct to enable easier
correlation between interface and PTP device.

Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Matthew Vick <matthew.vick@intel.com>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>