userns: Convert the audit loginuid  to be a kuid

Always store audit loginuids in type kuid_t.

Print loginuids by converting them into uids in the appropriate user
namespace, and then printing the resulting uid.

Modify audit_get_loginuid to return a kuid_t.

Modify audit_set_loginuid to take a kuid_t.

Modify /proc/<pid>/loginuid on read to convert the loginuid into the
user namespace of the opener of the file.

Modify /proc/<pid>/loginud on write to convert the loginuid
rom the user namespace of the opener of the file.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Paul Moore <paul@paul-moore.com> ?
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/include/net/netlabel.h b/include/net/netlabel.h
index f674409..2c95d55 100644
--- a/include/net/netlabel.h
+++ b/include/net/netlabel.h
@@ -110,7 +110,7 @@
 /* NetLabel audit information */
 struct netlbl_audit {
 	u32 secid;
-	uid_t loginuid;
+	kuid_t loginuid;
 	u32 sessionid;
 };