i40e: Add ablitity to enable/disable link from set_link_restart_an

The ability is already there in the fw and this will make it easy
to toggle link without calling set_phy_config when no other link
settings need to change.

Change-ID: I185567ae81776382ac145247e4eb1ee95f22382c
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>