usb_ep_alloc_request — allocate a request object to use with this endpoint
the endpoint to be used with with the request
GFP_* flags to use
Request objects must be allocated with this call, since they normally need controller-specific setup and may even need endpoint-specific resources such as allocation of DMA descriptors. Requests may be submitted with usb_ep_queue, and receive a single completion callback. Free requests with usb_ep_free_request, when they are no longer needed.
Returns the request, or null if one could not be allocated.