net: add real socket cookies

A long standing problem in netlink socket dumps is the use
of kernel socket addresses as cookies.

1) It is a security concern.

2) Sockets can be reused quite quickly, so there is
   no guarantee a cookie is used once and identify
   a flow.

3) request sock, establish sock, and timewait socks
   for a given flow have different cookies.

Part of our effort to bring better TCP statistics requires
to switch to a different allocator.

In this patch, I chose to use a per network namespace 64bit generator,
and to use it only in the case a socket needs to be dumped to netlink.
(This might be refined later if needed)

Note that I tried to carry cookies from request sock, to establish sock,
then timewait sockets.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eric Salo <salo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index eb16c7b..e565afd 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -77,6 +77,8 @@
 #define ir_v6_rmt_addr		req.__req_common.skc_v6_daddr
 #define ir_v6_loc_addr		req.__req_common.skc_v6_rcv_saddr
 #define ir_iif			req.__req_common.skc_bound_dev_if
+#define ir_cookie		req.__req_common.skc_cookie
+#define ireq_net		req.__req_common.skc_net
 
 	kmemcheck_bitfield_begin(flags);
 	u16			snd_wscale : 4,