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>

net/dccp/diag.c

@@ -66,6 +66,7 @@ static const struct inet_diag_handler dccp_diag_handler = {
 	.dump_one	 = dccp_diag_dump_one,
 	.idiag_get_info	 = dccp_diag_get_info,
 	.idiag_type	 = IPPROTO_DCCP,
+	.idiag_info_size = sizeof(struct tcp_info),
 };
 
 static int __init dccp_diag_init(void)