LU-2634 ldiskfs: clear extent flag for fast symlink

LU-2634 ldiskfs: clear extent flag for fast symlink

Fast symlinks on MDT filesystems formatted with the "extents" feature
are created with EXT4_EXTENTS_FL. e2fsck considers this a corruption
and deletes the symlink.

The patch is to clear extent flag in osd_ldiskfs_writelink() just as
ext4_symlink() does.

Signed-off-by: Liu Ying <emoly.liu@intel.com>
Change-Id: Ic0c711cc82de140f86baa71bacd1721fd4a19e07
Reviewed-on: http://review.whamcloud.com/5458
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>