sock_diag: specify info_size per inet protocol

Previously, there was no clear distinction between the inet protocols
that used struct tcp_info to report information and those that didn't.
This change adds a specific size attribute to the inet_diag_handler
struct which defines these interfaces.  This will make dispatching
sock_diag get_info requests identical for all inet protocols in a
following patch.

Tested: ss -au
Tested: ss -at
Signed-off-by: Craig Gallek <kraig@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/inet_diag.h

@@ -24,6 +24,7 @@ struct inet_diag_handler {
 					  struct inet_diag_msg *r,
 					  void *info);
 	__u16		idiag_type;
+	__u16		idiag_info_size;
 };
 
 struct inet_connection_sock;