tcp: prepare CC get_info() access from getsockopt()

We would like that optional info provided by Congestion Control
modules using netlink can also be read using getsockopt()

This patch changes get_info() to put this information in a buffer,
instead of skb, like tcp_get_info(), so that following patch
can reuse this common infrastructure.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/inet_diag.h b/include/uapi/linux/inet_diag.h
index d65c0a0..c7093c7 100644
--- a/include/uapi/linux/inet_diag.h
+++ b/include/uapi/linux/inet_diag.h
@@ -143,4 +143,8 @@
 	__u32	dctcp_ab_tot;
 };
 
+union tcp_cc_info {
+	struct tcpvegas_info	vegas;
+	struct tcp_dctcp_info	dctcp;
+};
 #endif /* _UAPI_INET_DIAG_H_ */