net: xfrmi: implement header_ops->parse_protocol for AF_PACKET

The xfrm interface uses skb->protocol to determine packet type, and
bails out if it's not set. For AF_PACKET injection, we need to support
its call chain of:

    packet_sendmsg -> packet_snd -> packet_parse_headers ->
      dev_parse_header_protocol -> parse_protocol

Without a valid parse_protocol, this returns zero, and xfrmi rejects the
skb. So, this wires up the ip_tunnel handler for layer 3 packets for
that case.
Reported-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/xfrm/xfrm_interface.c

@@ -37,6 +37,7 @@
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/ip6_route.h>
+#include <net/ip_tunnels.h>
 #include <net/addrconf.h>
 #include <net/xfrm.h>
 #include <net/net_namespace.h>
@@ -581,6 +582,7 @@ static const struct net_device_ops xfrmi_netdev_ops = {
 static void xfrmi_dev_setup(struct net_device *dev)
 {
 	dev->netdev_ops 	= &xfrmi_netdev_ops;
+	dev->header_ops		= &ip_tunnel_header_ops;
 	dev->type		= ARPHRD_NONE;
 	dev->mtu		= ETH_DATA_LEN;
 	dev->min_mtu		= ETH_MIN_MTU;