Only send Neighbours if we have some to send. (#7493)

* Only send Neighbours if we have some to send.

The original intent of NeighborInfo was that when a NeighbourInfo
was sent all of the nodes that saw it would reply with NeighbourInfo.
So, NeighbourInfo was sent even if there were no hop-zero nodes in
the NodeDB.

Since 2023, when this was implemented, our understanding of running city-wide
meshes has improved substantially. We have taken steps to reduce the impact
of NeighborInfo over LoRa.

This change aligns with those ideas: we will now only send NeighborInfo
if we have some neighbors to contribute.

The impact of this change is that a node must first see another directly
connected node in another packet type before NeighborInfo is sent. This means
that a node with no neighbors is no longer able to trigger other nodes
to broadcast NeighborInfo. It will, however, receive the regular periodic
broadcast of NeighborInfo, and will be able to send NeighborInfo if it
has at least 1 neighbor.

* Include all the things

* AvOid memleak

src/modules/NeighborInfoModule.cpp

@@ -105,14 +105,15 @@ void NeighborInfoModule::sendNeighborInfo(NodeNum dest, bool wantReplies)
 {
     meshtastic_NeighborInfo neighborInfo = meshtastic_NeighborInfo_init_zero;
     collectNeighborInfo(&neighborInfo);
-    meshtastic_MeshPacket *p = allocDataProtobuf(neighborInfo);
-    // send regardless of whether or not we have neighbors in our DB,
-    // because we want to get neighbors for the next cycle
-    p->to = dest;
-    p->decoded.want_response = wantReplies;
-    p->priority = meshtastic_MeshPacket_Priority_BACKGROUND;
-    printNeighborInfo("SENDING", &neighborInfo);
-    service->sendToMesh(p, RX_SRC_LOCAL, true);
+    // only send neighbours if we have some to send
+    if (neighborInfo.neighbors_count > 0) {
+        meshtastic_MeshPacket *p = allocDataProtobuf(neighborInfo);
+        p->to = dest;
+        p->decoded.want_response = wantReplies;
+        p->priority = meshtastic_MeshPacket_Priority_BACKGROUND;
+        printNeighborInfo("SENDING", &neighborInfo);
+        service->sendToMesh(p, RX_SRC_LOCAL, true);
+    }
 }
 
 /*
@@ -214,4 +215,4 @@ meshtastic_Neighbor *NeighborInfoModule::getOrCreateNeighbor(NodeNum originalSen
         neighbors.push_back(new_nbr);
     }
     return &neighbors.back();
-}
+}