ixgb: finish conversion to ndo_fix_features

Finish conversion to unified ethtool ops: convert get_flags.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>