Event mode: Enforce reliable hop limit and disallow default public MQTT (#4343)

* Event mode: Enforce reliable hop limit

* Event mode: Short circuit wantsLink on MQTT for default broker address

* Just enforce at channels level since everything uses this

* For events never forward packets with excessive hop_limit

* In EVENT_MODE, don't respond with hop_limit set more then the configured max.

* Correct hop_start when correcting hop_limit in event mode.

* Make EVENT_MODE work from userPrefs.h

* Event mode: Disallow Router or Repeater roles

---------

Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

src/mesh/Channels.cpp

@@ -1,6 +1,7 @@
 #include "Channels.h"
 #include "../userPrefs.h"
 #include "CryptoEngine.h"
+#include "Default.h"
 #include "DisplayFormatters.h"
 #include "NodeDB.h"
 #include "RadioInterface.h"
@@ -276,6 +277,12 @@ void Channels::setChannel(const meshtastic_Channel &c)
 
 bool Channels::anyMqttEnabled()
 {
+#if EVENT_MODE
+    // Don't publish messages on the public MQTT broker if we are in event mode
+    if (strcmp(moduleConfig.mqtt.address, default_mqtt_address) == 0) {
+        return false;
+    }
+#endif
     for (int i = 0; i < getNumChannels(); i++)
         if (channelFile.channels[i].role != meshtastic_Channel_Role_DISABLED && channelFile.channels[i].has_settings &&
             (channelFile.channels[i].settings.downlink_enabled || channelFile.channels[i].settings.uplink_enabled))