[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: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/inet_connection_sock.c

@@ -55,6 +55,13 @@ int inet_csk_bind_conflict(const struct sock *sk,
 	struct hlist_node *node;
 	int reuse = sk->sk_reuse;
 
+	/*
+	 * Unlike other sk lookup places we do not check
+	 * for sk_net here, since _all_ the socks listed
+	 * in tb->owners list belong to the same net - the
+	 * one this bucket belongs to.
+	 */
+
 	sk_for_each_bound(sk2, node, &tb->owners) {
 		if (sk != sk2 &&
 		    !inet_v6_ipv6only(sk2) &&

net/ipv6/inet6_connection_sock.c

@@ -33,6 +33,10 @@ int inet6_csk_bind_conflict(const struct sock *sk,
 	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 ||