sysctl: move security keys sysctl registration to its own file

The security keys sysctls are already declared on its own file,
just move the sysctl registration to its own file to help avoid
merge conflicts on sysctls.c, and help with clearing up sysctl.c
further.

This creates a small penalty of 23 bytes:

./scripts/bloat-o-meter vmlinux.1 vmlinux.2
add/remove: 2/0 grow/shrink: 0/1 up/down: 49/-26 (23)
Function                                     old     new   delta
init_security_keys_sysctls                     -      33     +33
__pfx_init_security_keys_sysctls               -      16     +16
sysctl_init_bases                             85      59     -26
Total: Before=21256937, After=21256960, chg +0.00%

But soon we'll be saving tons of bytes anyway, as we modify the
sysctl registrations to use ARRAY_SIZE and so we get rid of all the
empty array elements so let's just clean this up now.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

include/linux/key.h

@@ -490,9 +490,6 @@ do {									\
 	rcu_assign_pointer((KEY)->payload.rcu_data0, (PAYLOAD));	\
 } while (0)
 
-#ifdef CONFIG_SYSCTL
-extern struct ctl_table key_sysctls[];
-#endif
 /*
  * the userspace interface
  */

kernel/sysctl.c

@@ -2322,10 +2322,6 @@ static struct ctl_table vm_table[] = {
 int __init sysctl_init_bases(void)
 {
 	register_sysctl_init("kernel", kern_table);
-#ifdef CONFIG_KEYS
-	register_sysctl_init("kernel/keys", key_sysctls);
-#endif
-
 	register_sysctl_init("vm", vm_table);
 
 	return 0;

security/keys/sysctl.c

@@ -68,3 +68,10 @@ struct ctl_table key_sysctls[] = {
 #endif
 	{ }
 };
+
+static int __init init_security_keys_sysctls(void)
+{
+	register_sysctl_init("kernel/keys", key_sysctls);
+	return 0;
+}
+early_initcall(init_security_keys_sysctls);