LU-13157 mdd: migrate readlink from wrong place

In osd_read(), if symlink name buf length is smaller than i_size,
return -EOVERFLOW, and compare inline data length with i_size
instead of buflen.

Updated sanity.sh 230b.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Ia13b1f1079efc4ebd22ec400f1a909ff7ec2095d
Reviewed-on: https://review.whamcloud.com/37285
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>