geneve: expose gso partial features for tunnel offload

geneve: expose gso partial features for tunnel offload

GSO partial features for tunnels do not require any kind of support from
the underlying device: we can safely add them to the geneve UDP tunnel.

The only point of attention is the skb required features propagation in
the device xmit op: partial features must be stripped, except for
UDP_TUNNEL*.

Keep partial features disabled by default.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/d851ca8e928cf05d68310bcbaeaa5e9e0b01e058.1769011015.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>