mqueue: revert bump up DFLT_*MAX

Mqueue limitation is slightly naieve parameter likes other ipcs because
unprivileged user can consume kernel memory by using ipcs.

Thus, too aggressive raise bring us security issue. Example, current
setting allow evil unprivileged user use 256GB (= 256 * 1024 * 1024*1024)
and it's enough large to system will belome unresponsive. Don't do that.

Instead, every admin should adjust the knobs for their own systems.

Signed-off-by: KOSAKI Motohiro <[e-mail]>
Acked-by: Doug Ledford <[e-mail]>
Acked-by: Joe Korty <[e-mail]>
Cc: Amerigo Wang <[e-mail]>
Acked-by: Serge E. Hallyn <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Manfred Spraul <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/ipc_namespace.h

···
 #define DFLT_QUEUESMAX		      256
 #define HARD_QUEUESMAX		     1024
 #define MIN_MSGMAX			1
-#define DFLT_MSG		       64U
-#define DFLT_MSGMAX		     1024
+#define DFLT_MSG		       10U
+#define DFLT_MSGMAX		       10
 #define HARD_MSGMAX		    65536
 #define MIN_MSGSIZEMAX		      128
 #define DFLT_MSGSIZE		     8192U
-#define DFLT_MSGSIZEMAX	       (1024*1024)
+#define DFLT_MSGSIZEMAX		     8192
 #define HARD_MSGSIZEMAX	    (16*1024*1024)
 #else
 static inline int mq_init_ns(struct ipc_namespace *ns) { return 0; }