xfs: don't validate error tags in the I/O path

xfs: don't validate error tags in the I/O path

Source kernel commit: b8862a09d8256a9037293f1da3b4617b21de26f1

We can trust XFS developers enough to not pass random stuff to
XFS_ERROR_TEST/DELAY.  Open code the validity check in xfs_errortag_add,
which is the only place that receives unvalidated error tag values from
user space, and drop the now pointless xfs_errortag_enabled helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>