Use the hop_limit field of MeshPacket to limit max delivery depth in

the mesh.

src/mesh/MeshTypes.h

@@ -14,6 +14,15 @@ typedef uint8_t PacketId; // A packet sequence number
 #define ERRNO_NO_INTERFACES 33
 #define ERRNO_UNKNOWN 32 // pick something that doesn't conflict with RH_ROUTER_ERROR_UNABLE_TO_DELIVER
 
+/**
+ * the max number of hops a message can pass through, used as the default max for hop_limit in MeshPacket.
+ *
+ * We reserve 3 bits in the header so this could be up to 7, but given the high range of lora and typical usecases, keeping
+ * maxhops to 3 should be fine for a while.  This also serves to prevent routing/flooding attempts to be attempted for
+ * too long.
+ **/
+#define HOP_MAX 3
+
 typedef int ErrorCode;
 
 /// Alloc and free packets to our global, ISR safe pool