net: added netdevice operation for Tx

Added ndo_xsk_async_xmit. This ndo "kicks" the netdev to start to pull
userland AF_XDP Tx frames from a NAPI context.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/netdevice.h

@@ -1387,6 +1387,8 @@ struct net_device_ops {
 	int			(*ndo_xdp_xmit)(struct net_device *dev, int n,
 						struct xdp_frame **xdp,
 						u32 flags);
+	int			(*ndo_xsk_async_xmit)(struct net_device *dev,
+						      u32 queue_id);
 };
 
 /**