node_exporter: Disable ARP netlink collector

It currently fails (logging an error message on every scrape). This
disables the netlink collector, making it fall back to reading ARP
entries from /proc/net/arp.

modules/prometheus/node_exporter.nix

@@ -8,7 +8,10 @@
     enable = config.sbruder.wireguard.home.enable;
     listenAddress = config.sbruder.wireguard.home.address;
     enabledCollectors = [ "systemd" ];
-    disabledCollectors = [ "rapl" ];
+    disabledCollectors = [
+      "arp.netlink" # https://github.com/prometheus/node_exporter/issues/2849
+      "rapl"
+    ];
   };
 
   systemd.services.prometheus-node-exporter.after = [ "wireguard-wg-home.service" ];