net: tun: record RX queue in skb before do_xdp_generic()

This allows netif_receive_generic_xdp() to correctly determine the RX
queue from which the skb is coming, so that the context passed to the
XDP program will contain the correct RX queue index.

Signed-off-by: Gilberto Bertin <me@jibi.io>
Signed-off-by: David S. Miller <davem@davemloft.net>