Currently ST_OK and ST_NA are the only values defined to communicate
status of a request from a client. Add more error codes to clearly
indicate what failed. For example, when client sends request to import
a device that isn't export-able, server can send a specific error code
to the client.

Existing defines are moved to a common header in libsrc to be included
in the libusbip_la-usbip_common.o to be used by all the usbip tools.
Supporting interface to print error strings is added to the common lib.
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>