l2tp: consider '::' as wildcard address in l2tp_ip6 socket lookup

An L2TP socket bound to the unspecified address should match with any
address. If not, it can't receive any packet and __l2tp_ip6_bind_lookup()
can't prevent another socket from binding on the same device/tunnel ID.

While there, rename the 'addr' variable to 'sk_laddr' (local addr), to
make following patch clearer.
Signed-off-by: NGuillaume Nault <g.nault@alphalink.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip6.c

@@ -64,7 +64,7 @@ static struct sock *__l2tp_ip6_bind_lookup(struct net *net,
 	struct sock *sk;
 
 	sk_for_each_bound(sk, &l2tp_ip6_bind_table) {
-		const struct in6_addr *addr = inet6_rcv_saddr(sk);
+		const struct in6_addr *sk_laddr = inet6_rcv_saddr(sk);
 		struct l2tp_ip6_sock *l2tp = l2tp_ip6_sk(sk);
 
 		if (l2tp == NULL)
@@ -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)) &&
+		    (!sk_laddr || ipv6_addr_any(sk_laddr) || ipv6_addr_equal(sk_laddr, laddr)) &&
 		    (!sk->sk_bound_dev_if || !dif ||
 		     sk->sk_bound_dev_if == dif))
 			goto found;