Fixed a possibility that the function handler might be called twice

Fixed a possibility that the function handler might be called twice

Configfs can use more than one configs.
(/sys/kernel/config/usb_gadget/hal-gadget/configs/hal-config.1 and /sys/kernel/config/usb_gadget/hal-gadget/configs/hal-config.2)

One usb function can be included in two config simultaneously.
In this situation, a handler associated with function can be called twice for a usb function.

To prevent duplicate calls,
it handles only the handlers of functions enabled in configfs, not the usb functions included in all configs.

Change-Id: I5e02dadc5d2688f0ad9210ad5ab149fb95ab05ba