MXS-3051: Show connection TLS cipher

This tells the user whether a session is using TLS or not. Currently, only
the client TLS cipher is shown in MaxCtrl as the backend ciphers require
additional formatting.

server/core/session.cc

@@ -876,6 +876,7 @@ json_t* session_json_data(const Session* session, const char* host)
     }
 
     json_object_set_new(attr, "connections", dcb_arr);
+    json_object_set_new(attr, "client", dcb_to_json(session->client_dcb));
 
     json_t* queries = session->queries_as_json();
     json_object_set_new(attr, "queries", queries);