core: when probing mark ports as AT capable too

On a ZTE MF626, sometimes the aux port will respond only with
"ERROR" to probing commands (while the SIM is starting up) and
previously we'd lose the port because we were only looking for
valid probe responses.  But if the port returns ERROR or CME ERROR
etc we know it's an AT port and that we can use it once we've
gotten the type response (CDMA or GSM) from the main port.

plugins/mm-plugin-zte.c

@@ -49,6 +49,8 @@ get_level_for_capabilities (guint32 capabilities)
         return 10;
     if (capabilities & MM_PLUGIN_BASE_PORT_CAP_QCDM)
         return 10;
+    if (capabilities & MM_PLUGIN_BASE_PORT_CAP_AT)
+        return 10;
     return 0;
 }