ixgbe: Fix link issues caused by a reset while interface is down

Interface fails to obtain link on 82599 SFP in the following scenario:

1. Set advertised speed to GB:
ethtool -s eth0 advertise 0x20

2. Bring interface down
ip link set eth0 down

3. Issue any command that leads to a reset:
ethtool -t eth0

4. Bring link back up:
ip link set eth0 up

Following patch makes sure that the driver flaps the Tx laser every time
ixgbe_start_hw() is called, and not only when the speed is set.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>