gve: Wrap struct xdp_buff

gve: Wrap struct xdp_buff

RX timestamping will need to keep track of extra temporary information
per-packet. In preparation for this, introduce gve_xdp_buff to wrap the
xdp_buff. This is similar in function to stmmac_xdp_buff and
ice_xdp_buff.

Signed-off-by: Tim Hostetler <thostet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
Link: https://patch.msgid.link/20251114211146.292068-3-joshwash@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>