Mark packets received via MQTT and add option to ignore them (#3117)

* Mark packets received via MQTT and add option to ignore them

* Don't send packets received via MQTT back into MQTT
Generate implicit ACK for packets we as an MQTT gateway sent

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Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/RadioInterface.h

@@ -12,6 +12,7 @@
 
 #define PACKET_FLAGS_HOP_MASK 0x07
 #define PACKET_FLAGS_WANT_ACK_MASK 0x08
+#define PACKET_FLAGS_VIA_MQTT_MASK 0x10
 
 /**
  * This structure has to exactly match the wire layout when sent over the radio link.  Used to keep compatibility
@@ -223,4 +224,4 @@ class RadioInterface
 };
 
 /// Debug printing for packets
-void printPacket(const char *prefix, const meshtastic_MeshPacket *p);
+void printPacket(const char *prefix, const meshtastic_MeshPacket *p);