nfp: add offloads on representors

FW/HW can generally support the standard networking offloads
on representors without any trouble.  Add the ability for FW
to advertise which features should be available on representors.

Because representors are muxed on top of the vNIC we need to listen
on feature changes of their lower devices, and update their features
appropriately.

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