LU-17055 ldiskfs: add falloc(zero) for OST/ext

LU-17055 ldiskfs: add falloc(zero) for OST/ext

This patch implements falloc(FALLOC_FL_ZERO_RANGE)
on the ldiskfs backend.

Here, we just follow the implementation of "LU-10048 osd:
async truncate" where we as well execute zeroing outside
of main transaction handle, to avoids restarting zeroing
transaction handles in main transaction.

NOTE: this is the 1st part of falloc(zero) where it functions
only on ldiskfs-extend. To address DoM/indirect part another
patch will be added.

Signed-off-by: Keguang Xu <squalfof@gmail.com>
Change-Id: I76310546715f96872bf4dd441beb453ee4ac0abe
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57763
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>