This adds an early exit when the usb interface with the data endpoints
is not activated. This prevents the cdc_ecm_netdev code from attempting
to send the PDU when the USB device is not yet initialized or activated
by a host.
This commit changes the name of the requests over the control endpoints
to control requests instead of setup requests. This is a terminology fix
to follow the USB specification more closely as technically only the
first stage of a control request is named setup which contains a setup
packet. The whole transfer is a control transfer.