hnbgw: Bring all parts together

We now have the RUA and SUA parts interconnected by the
context ID mapper, and should be able to pass messages back and forward
between both sides.

Unfortunately this touches a bit of everything, but the structures are
all still very much in flux.  Hopefully they will start to stabilize at
some point soon...
diff --git a/src/hnbgw_cn.h b/src/hnbgw_cn.h
new file mode 100644
index 0000000..2599fd3
--- /dev/null
+++ b/src/hnbgw_cn.h
@@ -0,0 +1,5 @@
+#pragma once
+
+#include "hnbgw.h"
+
+struct hnbgw_cnlink *hnbgw_cnlink_init(struct hnb_gw *gw, const char *host, uint16_t port);