LU-13983 llite: rmdir releases inode on client

LU-13983 llite: rmdir releases inode on client

Same as file unlink, rmdir should release inode on client, to achieve
this, ll_rmdir() update inode i_nlink after rmdir, then the last
iput() will release the inode.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I9181151de1830b48986afec30c83120e9f112a85
Reviewed-on: https://review.whamcloud.com/40011
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>