9p: make cryptic unknown error from server less scary

Right now when we get an error string from the server that we can't
map we report a cryptic error that actually makes it look like we are
reporting a problem with the client.  This changes the text of the log
message to clarify where the error is coming from.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
1 file changed