l2tp: Fix sendmsg() return value

PPPoL2TP sockets should comply with the standard send*() return values
(i.e. return number of bytes sent instead of 0 upon success).
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -358,7 +358,7 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
 	sock_put(ps->tunnel_sock);
 	sock_put(sk);
 
-	return error;
+	return total_len;
 
 error_put_sess_tun:
 	sock_put(ps->tunnel_sock);