nfp: support VxLAN inner TSO with GSO_PARTIAL offload

nfp: support VxLAN inner TSO with GSO_PARTIAL offload

VxLAN belongs to UDP-based encapsulation protocol. Inner TSO for VxLAN
packet with udpcsum requires offloading of outer header csum.

The device doesn't support outer header csum offload. However, inner TSO
for VxLAN with udpcsum can still work with GSO_PARTIAL offload, which
means outer udp csum computed by stack and inner tcp segmentation finished
by hardware. Thus, the patch enable features "NETIF_F_GSO_UDP_TUNNEL_CSUM"
and "NETIF_F_GSO_PARTIAL" and set gso_partial_features.

Signed-off-by: Fei Qin <fei.qin@corigine.com>
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20220430231150.175270-1-simon.horman@corigine.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>