nfp: flower: use geneve and vxlan helpers

Make use of the recently added VXLAN and geneve helper functions to
determine the type of the netdev from its rtnl_link_ops.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>