nfp: add .ndo_init() and .ndo_uninit() callbacks

BPF code should unregister the offload capabilities from .ndo_uninit(),
to make sure the operation is atomic with unlist_netdevice().  Plumb
the init/uninit NDOs for vNICs and representors.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>