Don't prevent network changes if can't save

If the filesystem is messed up for some reason and the network
configuration couldn't be saved, the network configuration change was
aborted. This could be worked around by not saving the configuration.
However, this seemed like the wrong way to degrade. This commit changes
the logic to allow the network configuration, but log an error. The
configuration will be lost on a reboot, but perhaps it will help someone
debug and fix the device that's having trouble.

lib/vintage_net/interface.ex

@@ -109,7 +109,7 @@ defmodule VintageNet.Interface do
          :ok <- PredictableInterfaceName.precheck(ifname),
          normalized_config = raw_config.source_config,
          :changed <- configuration_changed(ifname, normalized_config),
-         :ok <- persist_configuration(ifname, normalized_config, options),
+         persist_configuration(ifname, normalized_config, options),
          PropertyTable.put(VintageNet, ["interface", ifname, "config"], normalized_config),
          {:error, :already_started} <- maybe_start_interface(ifname) do
       GenStateMachine.call(via_name(raw_config.ifname), {:configure, raw_config})
@@ -124,13 +124,13 @@ defmodule VintageNet.Interface do
   end
 
   defp persist_configuration(ifname, normalized_config, options) do
-    case Keyword.get(options, :persist, true) do
-      true ->
-        Persistence.call(:save, [ifname, normalized_config])
-
-      false ->
-        :ok
+    if Keyword.get(options, :persist, true) do
+      with {:error, reason} <- Persistence.call(:save, [ifname, normalized_config]) do
+        log(:warn, ifname, "Error saving configuration: #{inspect(reason)}")
+      end
     end
+
+    :ok
   end
 
   defp maybe_start_interface(ifname) do
@@ -196,10 +196,10 @@ defmodule VintageNet.Interface do
     GenStateMachine.call(via_name(ifname), {:ioctl, command, args})
   end
 
-  defp debug(data, message), do: log(:debug, data, message)
+  defp debug(data, message), do: log(:debug, data.ifname, message)
 
-  defp log(level, data, message) do
-    Logger.log(level, ["VintageNet(", data.ifname, "): ", message])
+  defp log(level, ifname, message) do
+    Logger.log(level, ["VintageNet(", ifname, "): ", message])
   end
 
   @impl GenStateMachine