NetLabel: Add secid token support to the NetLabel secattr struct

This patch adds support to the NetLabel LSM secattr struct for a secid token
and a type field, paving the way for full LSM/SELinux context support and
"static" or "fallback" labels.  In addition, this patch adds a fair amount
of documentation to the core NetLabel structures used as part of the
NetLabel kernel API.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Signed-off-by: James Morris <jmorris@namei.org>

net/netlabel/netlabel_unlabeled.c

@@ -241,6 +241,7 @@ int netlbl_unlabel_getattr(struct netlbl_lsm_secattr *secattr)
 	if (netlabel_unlabel_acceptflg == 0)
 		return -ENOMSG;
 	netlbl_secattr_init(secattr);
+	secattr->type = NETLBL_NLTYPE_UNLABELED;
 	return 0;
 }