iavf: rely on netdev's own registered state

iavf: rely on netdev's own registered state

The information whether a netdev has been registered is already present
in the netdev itself. There's no need for a driver flag with the same
meaning.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231027175941.1340255-6-jacob.e.keller@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>