i40e: Fix order of checks when enabling/disabling autoneg in ethtool

We were previously checking if autoneg was allowed to change before
checking if autoneg was changing. We need to do this in the other order
or else we will erroneously return EINVAL when autoneg is not changing.

Change-ID: Iff9f7d1c9bddc1ad1e5d227d4f42754f90155410
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>