Currently we don't check the error_tag when someone's trying to set up
error injection testing. If userspace passes in a value we don't know
about, send back an error. This will help xfstests to _notrun a test
that uses error injection to test things like log replay.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Dave Chinner <david@fromorbit.com>