[SOCK]: Add some notes about per-bind-bucket sock lookup.

I was asked about "why don't we perform a sk_net filtering in
bind_conflict calls, like we do in other sock lookup places"
for a couple of times.

Can we please add a comment about why we do not need one?

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c
index 78de42a..87801cc 100644
--- a/net/ipv6/inet6_connection_sock.c
+++ b/net/ipv6/inet6_connection_sock.c
@@ -33,6 +33,10 @@
 	const struct hlist_node *node;
 
 	/* We must walk the whole port owner list in this case. -DaveM */
+	/*
+	 * See comment in inet_csk_bind_conflict about sock lookup
+	 * vs net namespaces issues.
+	 */
 	sk_for_each_bound(sk2, node, &tb->owners) {
 		if (sk != sk2 &&
 		    (!sk->sk_bound_dev_if ||