ixgb: fix interface losing macaddr on ifdn/up

user contributed fix for LAA across down/up, from tonychung00@users.sf.net.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: John Ronciak <john.ronciak@intel.com>