udp_diag: implement idiag_get_info for udp/udplite to get queue information

When we use netlink to monitor queue information for udp socket,
idiag_rqueue and idiag_wqueue of inet_diag_msg are returned with 0.

Keep consistent with netstat, just return back allocated rmem/wmem size.

Signed-off-by: Shan Wei <davidshan@tencent.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 8d25a1c..8f8db72 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -141,7 +141,7 @@
 			goto rtattr_failure;
 
 	if (icsk == NULL) {
-		r->idiag_rqueue = r->idiag_wqueue = 0;
+		handler->idiag_get_info(sk, r, NULL);
 		goto out;
 	}