userns: Teach inet_diag to work with user namespaces

Compute the user namespace of the socket that we are replying to
and translate the kuids of reported sockets into that user namespace.

Cc: Andrew Vagin <avagin@openvz.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/include/linux/inet_diag.h b/include/linux/inet_diag.h
index f1362b5..e788c18 100644
--- a/include/linux/inet_diag.h
+++ b/include/linux/inet_diag.h
@@ -159,6 +159,7 @@
 struct inet_connection_sock;
 int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 			      struct sk_buff *skb, struct inet_diag_req_v2 *req,
+			      struct user_namespace *user_ns,
 			      u32 pid, u32 seq, u16 nlmsg_flags,
 			      const struct nlmsghdr *unlh);
 void inet_diag_dump_icsk(struct inet_hashinfo *h, struct sk_buff *skb,