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.

plugins/mm-plugin-zte.c

@@ -93,6 +93,15 @@ supports_port (MMPluginBase *base,
     }
 
     /* Otherwise kick off a probe */
+
+    /* Many ZTE devices will flood the port with "Message waiting" indications
+     * and eventually fill up the serial buffer and crash.  We need to turn off
+     * that indicator.  See NetworkManager commits
+     * 	1235f71b20c92cded4abd976ccc5010649aae1a0 and
+     * 	f38ad328acfdc6ce29dd1380602c546b064161ae for more details.
+     */
+    mm_plugin_base_supports_task_set_custom_init_command (task, "ATE0+CPMS?", 3, 4, TRUE);
+
     if (mm_plugin_base_probe_port (base, task, NULL))
         return MM_PLUGIN_SUPPORTS_PORT_IN_PROGRESS;