igb: link up/down messages must follow a specific format

The system log messages created on a link status change need to follow a
specific format to work with tools some customers use.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>