namespaces: mqueue namespace: adapt sysctl

Largely inspired from ipc/ipc_sysctl.c.  This patch isolates the mqueue
sysctl stuff in its own file.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/Kconfig

@@ -208,6 +208,12 @@ config POSIX_MQUEUE
 
 	  If unsure, say Y.
 
+config POSIX_MQUEUE_SYSCTL
+	bool
+	depends on POSIX_MQUEUE
+	depends on SYSCTL
+	default y
+
 config BSD_PROCESS_ACCT
 	bool "BSD Process Accounting"
 	help