Prepare for setting up the endpoints for usage.

NB: It seems that the Linux driver setups the endpoints "live".
This seems contrary to how e.g. uath in FreeBSD setup the endpoints,
by declaring them in a const structure in advance.

* Added enum for all endpoints used by ath6kl;
* Added function ath6kl_usb_setup_xfer_resources that prints out
type of every endpoint associated to the current interface;