inet_diag: Export inet diag cookie checking routine

The netlink diag susbsys stores sk address bits in the nl message
as a "cookie" and uses one when dumps details about particular
socket.

The same will be required for udp diag module, so introduce a heler
in inet_diag module

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 851feff..5036747 100644
--- a/include/linux/inet_diag.h
+++ b/include/linux/inet_diag.h
@@ -144,6 +144,8 @@
 	__u16                   idiag_type;
 };
 
+int inet_diag_check_cookie(struct sock *sk, struct inet_diag_req *req);
+
 extern int  inet_diag_register(const struct inet_diag_handler *handler);
 extern void inet_diag_unregister(const struct inet_diag_handler *handler);
 #endif /* __KERNEL__ */