zte: handle unsolicited messages during probe

This implements the same fixes that NetworkManager's 0.7 branch
implemented in commits f38ad328acfdc6ce29dd1380602c546b064161ae and
1235f71b20c92cded4abd976ccc5010649aae1a0.  Many ZTE devices will
spam the port with messages about waiting voicemail/SMS which buffer
up and cause the device to eventually crash if not suppressed.

src/mm-plugin-base.h

@@ -68,6 +68,11 @@ guint32 mm_plugin_base_supports_task_get_probed_capabilities (MMPluginBaseSuppor
 void mm_plugin_base_supports_task_complete (MMPluginBaseSupportsTask *task,
                                             guint32 level);
 
+void mm_plugin_base_supports_task_set_custom_init_command (MMPluginBaseSupportsTask *task,
+                                                           const char *cmd,
+                                                           guint32 delay_seconds,
+                                                           guint32 max_tries,
+                                                           gboolean fail_if_timeout);
 
 #define MM_TYPE_PLUGIN_BASE            (mm_plugin_base_get_type ())
 #define MM_PLUGIN_BASE(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), MM_TYPE_PLUGIN_BASE, MMPluginBase))