Use the X-AnyConnect-Identifier-Platform header to identify mobile clients

That is, if the header contains "android" or "apple-ios" mark it as
a mobile client. The header X-AnyConnect-Identifier-DeviceType is only
considered for logging purposes and appended to the user-agent name
if present.

src/worker-vpn.c

@@ -754,6 +754,10 @@ void session_info_send(worker_st * ws)
 		msg.user_agent = ws->req.user_agent;
 	}
 
+	if (ws->req.devtype[0] != 0) {
+		msg.device_type = ws->req.devtype;
+	}
+
 	if (ws->req.hostname[0] != 0) {
 		msg.hostname = ws->req.hostname;
 	}