MFC 259240

MFC 259240
   sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
        When a da or ada device dissappears, outstanding IOs fail with
        ENXIO, not EIO.  The check for EIO was probably copied from Illumos,
        where that is indeed the correct errno.

        Without this change, pulling a busy drive from a zpool would usually
        turn it into UNAVAIL, even though pulling an idle drive would turn
        it into REMOVED.  With this change, it is REMOVED every time.

        Also, vdev_geom_io_intr shouldn't do zfs_post_remove, because that
        results in devd getting two resource.fs.zfs.removed events.  The
        comment said that the event had to be sent directly instead of
        through the async removal thread because "the DE engine is using
        this information to discard prevoius I/O errors".  However, the fact
        that vdev_geom_io_intr was never actually sending the events until
        now, and that vdev_geom_orphan never sent them at all, and that
        vdev_geom_orphan usually gets called about 2 seconds after the
        actual removal, means that FreeBSD's userland can cope with a late
        event just fine.

git-svn-id: svn://svn.freebsd.org/base/stable/9@260518 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f