ixgbe: Be more careful when modifying MAC filters

This change makes it so that we are much more explicit about the ordering
of updates to the receive address register (RAR) table. Prior to this patch
I believe we may have been updating the table while entries were still
active, or possibly allowing for reordering of things since we weren't
explicitly flushing writes to either the lower or upper portion of the
register prior to accessing the other half.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>