At some points, some drivers can't report the full TX status
information. This can happen for the UNKNOWN state, or the
FAILURE state (in case the URB failed).
Add a wrapper function to simplify reporting the
empty TX information.
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>