LSM: Introduce LSM_FLAG_LEGACY_MAJOR

This adds a flag for the current "major" LSMs to distinguish them when
we have a universal method for ordering all LSMs. It's called "legacy"
since the distinction of "major" will go away in the blob-sharing world.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>

security/selinux/hooks.c

@@ -6999,6 +6999,7 @@ void selinux_complete_init(void)
    all processes and objects when they are created. */
 DEFINE_LSM(selinux) = {
 	.name = "selinux",
+	.flags = LSM_FLAG_LEGACY_MAJOR,
 	.init = selinux_init,
 };