ixgbe: fix link behavior for SFP+ when driver is brought down

We have had several requests to have ifconfig down command disable
the SFP+ laser and thus make link go down.  Likewise on ifconfig up
the laser would be enabled and link would come up.  This patch enables
that behavior.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>