netlabel: Initial support for the CALIPSO netlink protocol.

CALIPSO is a packet labelling protocol for IPv6 which is very similar
to CIPSO.  It is specified in RFC 5570.  Much of the code is based on
the current CIPSO code.

This adds support for adding passthrough-type CALIPSO DOIs through the
NLBL_CALIPSO_C_ADD command.  It requires attributes:

 NLBL_CALIPSO_A_TYPE which must be CALIPSO_MAP_PASS.
 NLBL_CALIPSO_A_DOI.

In passthrough mode the CALIPSO engine will map MLS secattr levels
and categories directly to the packet label.

At this stage, the major difference between this and the CIPSO
code is that IPv6 may be compiled as a module.  To allow for
this the CALIPSO functions are registered at module init time.

Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/net/netlabel/netlabel_mgmt.c b/net/netlabel/netlabel_mgmt.c
index b2aeb5d..975b1e9 100644
--- a/net/netlabel/netlabel_mgmt.c
+++ b/net/netlabel/netlabel_mgmt.c
@@ -674,6 +674,15 @@
 			goto protocols_return;
 		protos_sent++;
 	}
+#if IS_ENABLED(CONFIG_IPV6)
+	if (protos_sent == 2) {
+		if (netlbl_mgmt_protocols_cb(skb,
+					     cb,
+					     NETLBL_NLTYPE_CALIPSO) < 0)
+			goto protocols_return;
+		protos_sent++;
+	}
+#endif
 
 protocols_return:
 	cb->args[0] = protos_sent;