Fixed using wrong usb function list when usb gadget enable/disable in configfs

Fixed using wrong usb function list when usb gadget enable/disable in configfs

When usb gadget is enabled/disabled in configfs,
it retrieves the list of currently used usb functions in order to run the service handler.

Before the modification, it retrieve a list of "all functions" used even once.

So if you run "ifconfig" after changing usb mode to "sdb mode" -> "rndis mode" -> "sdb mode",
even in sdb mode, the usb0 network interface appears.

Change-Id: I83564591cd899197077823fdb2fbe25d034fcf46