ipv4: Fix ip_queue_xmit to pass sk into ip_local_out_sk

commit 850dcc4d upstream.

After a packet has been encapsulated by a tunnel we should use the
tunnel sockets local multicast loopback flag to control if the
encapsulated packet should be locally loopback back.

Pass sk into ip_local_out_sk so that in the rare case we are dealing
with a tunneled packet whose tunnel destination address is a multicast
address the kernel properly decides to loopback this packet.

In practice I don't think this matters as ip_queue_xmit is used by
tcp, l2tp and sctp none of which I am aware of uses ip level
multicasting as they are all point to point communications protocols.
Let's fix this before someone uses ip_queue_xmit for a tunnel protocol
that does use multicast.

Fixes: aad88724 ("ipv4: add a sock pointer to dst->output() path.")
Fixes: b0270e91 ("ipv4: add a sock pointer to ip_queue_xmit()")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/ipv4/ip_output.c

@@ -436,7 +436,7 @@ int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl)
 	skb->priority = sk->sk_priority;
 	skb->mark = sk->sk_mark;
 
-	res = ip_local_out(skb);
+	res = ip_local_out_sk(sk, skb);
 	rcu_read_unlock();
 	return res;