sock_diag: Introduce new message type

This type will run the family+protocol based socket dumping.
Also prepare the stub function for it.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/inet_diag.h b/include/linux/inet_diag.h
index abf5028..f7baaf6 100644
--- a/include/linux/inet_diag.h
+++ b/include/linux/inet_diag.h
@@ -6,6 +6,7 @@
 /* Just some random number */
 #define TCPDIAG_GETSOCK 18
 #define DCCPDIAG_GETSOCK 19
+#define SOCK_DIAG_BY_FAMILY 20
 
 #define INET_DIAG_GETSOCK_MAX 24