plugins: simplify custom init commands

Instead of having two places that custom init stuff got processed
(a hook in the MMPluginBase class itself and a callback too) just
use a callback, and simplify it somewhat so that the plugin tracks
how many tries it cares about and what to do based on the response
or error.

plugins/mm-plugin-zte.c

@@ -61,6 +61,22 @@ probe_result (MMPluginBase *base,
     mm_plugin_base_supports_task_complete (task, get_level_for_capabilities (capabilities));
 }
 
+static gboolean
+custom_init_response_cb (MMPluginBaseSupportsTask *task,
+                         GString *response,
+                         GError *error,
+                         guint32 tries,
+                         gboolean *out_fail,
+                         guint32 *out_level,
+                         gpointer user_data)
+{
+    if (error)
+        return tries <= 4 ? TRUE : FALSE;
+
+    /* No error, assume success */
+    return FALSE;
+}
+
 static MMPluginSupportsResult
 supports_port (MMPluginBase *base,
                MMModem *existing,
@@ -113,7 +129,11 @@ supports_port (MMPluginBase *base,
      * 	1235f71b20c92cded4abd976ccc5010649aae1a0 and
      * 	f38ad328acfdc6ce29dd1380602c546b064161ae for more details.
      */
-    mm_plugin_base_supports_task_set_custom_init_command (task, "ATE0+CPMS?", 3, 4, FALSE, NULL, NULL);
+    mm_plugin_base_supports_task_set_custom_init_command (task,
+                                                          "ATE0+CPMS?",
+                                                          3,
+                                                          custom_init_response_cb,
+                                                          NULL);
 
     if (mm_plugin_base_probe_port (base, task, 100000, NULL))
         return MM_PLUGIN_SUPPORTS_PORT_IN_PROGRESS;