staging: usbip: userspace: libsrc: replace numbers by ascii

replace numbers in code by ascii text constants as suggested
by Dan Carpenter:
http://driverdev.linuxdriverproject.org/pipermail/devel/2013-February/035907.html

Signed-off-by: Stefan Reif <ke42caxa@cip.cs.fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>