apparmor: add a kernel label to use on kernel objects

Separate kernel objects from unconfined. This is done so we can
distinguish between the two in debugging, auditing and in preparation
for being able to replace unconfined, which is not appropriate for the
kernel.

The kernel label will continue to behave similar to unconfined.

Acked-by: Jon Tourville <jon.tourville@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/policy_ns.h

@@ -74,6 +74,7 @@ struct aa_ns {
 	struct dentry *dents[AAFS_NS_SIZEOF];
 };
 
+extern struct aa_label *kernel_t;
 extern struct aa_ns *root_ns;
 
 extern const char *aa_hidden_ns_name;