LU-17042 target: allow fsmap ioctl

LU-17042 target: allow fsmap ioctl

Pass through the FS_IOC_GETFSMAP ioctl to the underlying ldiskfs
so e2freefrag can make use of online query.

Change-Id: Ia4f1fd3c0b02429b247fa71e73b4a95b98b47026
Test-Parameters: trivial
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52147
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>