Orangefs: Clean up error decoding.

Errors from the server need to be decoded. A bunch of code was imported from
the server to do this but much of it is convoluted and not even needed. The
result is better but still as convoluted as required by the protocol.

Signed-off-by: Martin Brandenburg <martin@omnibond.com>
Signed-off-by: Mike Marshall <hubcap@omnibond.com>