Forwarding plugin: force set the response ID to match the query ID

Shouldn't be necessary, but just to be safe in case `dns.Exchange()`
does something unexpected.

dnscrypt-proxy/plugin_forward.go

@@ -104,6 +104,7 @@ func (plugin *PluginForward) Eval(pluginsState *PluginsState, msg *dns.Msg) erro
 	if edns0 := respMsg.IsEdns0(); edns0 == nil || !edns0.Do() {
 		respMsg.AuthenticatedData = false
 	}
+	respMsg.Id = msg.Id
 	pluginsState.synthResponse = respMsg
 	pluginsState.action = PluginsActionSynth
 	pluginsState.returnCode = PluginsReturnCodeForward