ipv4: add a sock pointer to dst->output() path.

In the dst->output() path for ipv4, the code assumes the skb it has to
transmit is attached to an inet socket, specifically via
ip_mc_output() : The sk_mc_loop() test triggers a WARN_ON() when the
provider of the packet is an AF_PACKET socket.

The dst->output() method gets an additional 'struct sock *sk'
parameter. This needs a cascade of changes so that this parameter can
be propagated from vxlan to final consumer.

Fixes: 8f646c922d ("vxlan: keep original skb ownership")
Reported-by: lucien xin <lucien.xin@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/vxlan.c

@@ -1755,8 +1755,8 @@ int vxlan_xmit_skb(struct vxlan_sock *vs,
 	if (err)
 		return err;
 
-	return iptunnel_xmit(rt, skb, src, dst, IPPROTO_UDP, tos, ttl, df,
-			     false);
+	return iptunnel_xmit(vs->sock->sk, rt, skb, src, dst, IPPROTO_UDP,
+			     tos, ttl, df, false);
 }
 EXPORT_SYMBOL_GPL(vxlan_xmit_skb);