Fix pppol2tp getsockname()

While testing L2TP functionality, I came across a bug in getsockname().  The
IP address returned within the pppol2tp_addr's addr memember was not being
set to the IP  address in use.  This bug is caused by using inet_sk() on the
wrong socket (the L2TP socket rather than the underlying UDP socket), and was
likely introduced during the addition of L2TPv3 support.

Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -915,7 +915,7 @@ static int pppol2tp_getname(struct socket *sock, struct sockaddr *uaddr,
 		goto end_put_sess;
 	}
 
-	inet = inet_sk(sk);
+	inet = inet_sk(tunnel->sock);
 	if (tunnel->version == 2) {
 		struct sockaddr_pppol2tp sp;
 		len = sizeof(sp);