l2tp: fix address test in __l2tp_ip6_bind_lookup()

The '!(addr && ipv6_addr_equal(addr, laddr))' part of the conditional
matches if addr is NULL or if addr != laddr.
But the intend of __l2tp_ip6_bind_lookup() is to find a sockets with
the same address, so the ipv6_addr_equal() condition needs to be
inverted.

For better clarity and consistency with the rest of the expression, the
(!X || X == Y) notation is used instead of !(X && X != Y).

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip6.c

@@ -72,7 +72,7 @@ static struct sock *__l2tp_ip6_bind_lookup(struct net *net,
 
 		if ((l2tp->conn_id == tunnel_id) &&
 		    net_eq(sock_net(sk), net) &&
-		    !(addr && ipv6_addr_equal(addr, laddr)) &&
+		    (!addr || ipv6_addr_equal(addr, laddr)) &&
 		    (!sk->sk_bound_dev_if || !dif ||
 		     sk->sk_bound_dev_if == dif))
 			goto found;