Add Privilage violation error and handle errors properly rather than …

…returning blank strings

lib/scrub/cip.ex

@@ -1,5 +1,6 @@
 defmodule Scrub.CIP do
   def status_code(0x00), do: :success
   def status_code(0x06), do: :too_much_data
+  def status_code(0x0F), do: :privilage_violation
   def status_code(status), do: status
 end

lib/scrub/cip/connection_manager.ex

@@ -206,7 +206,7 @@ defmodule Scrub.CIP.ConnectionManager do
 
   defp decode_service(
          :unconnected_send,
-         %{size: _size},
+         %{status_code: :success},
          <<
            data::binary
          >>,
@@ -218,6 +218,15 @@ defmodule Scrub.CIP.ConnectionManager do
     end
   end
 
+  defp decode_service(
+         _,
+         %{status_code: code},
+         _,
+         _
+       ) do
+    {:error, code}
+  end
+
   defp large_forward_open_network_parameters(opts \\ []) do
     owner = opts[:owner] || 0
     connection_type = opts[:connection_type] || :point_to_point