misc/examples: check return code for has_totag() in kemi lua script

misc/examples/kemi/kamailio-basic-kemi-lua.lua

@@ -299,7 +299,7 @@ function ksr_route_natmanage()
 	KSR.rtpproxy.rtpproxy_manage("co");
 
 	if KSR.siputils.is_request()>0 then
-		if not KSR.siputils.has_totag() then
+		if KSR.siputils.has_totag()<0 then
 			if KSR.tmx.t_is_branch_route()>0 then
 				KSR.rr.add_rr_param(";nat=yes");
 			end