usb: gadget: f_mass_storage: Make us pass USBCV MSC Compliance tests

Defer the SET_CONFIG and SET_INTERFACE control transfer's data/status
stages till we are ready to process new CBW from the host. This way we
ensure that we don't loose any CBW during MSC compliance tests and cause
lock up.

Signed-off-by: Roger Quadros <roger.quadros@nokia.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>