tun: convert to use generic xdp_frame and xdp_return_frame API

The tuntap driver invented it's own driver specific way of queuing
XDP packets, by storing the xdp_buff information in the top of
the XDP frame data.

Convert it over to use the more generic xdp_frame structure.  The
main problem with the in-driver method is that the xdp_rxq_info pointer
cannot be trused/used when dequeueing the frame.

V3: Remove check based on feedback from Jason

Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
index fd00170..3d2996d 100644
--- a/include/linux/if_tun.h
+++ b/include/linux/if_tun.h
@@ -22,7 +22,7 @@
 #if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE)
 struct socket *tun_get_socket(struct file *);
 struct ptr_ring *tun_get_tx_ring(struct file *file);
-bool tun_is_xdp_buff(void *ptr);
+bool tun_is_xdp_frame(void *ptr);
 void *tun_xdp_to_ptr(void *ptr);
 void *tun_ptr_to_xdp(void *ptr);
 void tun_ptr_free(void *ptr);
@@ -39,7 +39,7 @@ static inline struct ptr_ring *tun_get_tx_ring(struct file *f)
 {
 	return ERR_PTR(-EINVAL);
 }
-static inline bool tun_is_xdp_buff(void *ptr)
+static inline bool tun_is_xdp_frame(void *ptr)
 {
 	return false;
 }