LU-15969 llite: add support for ->fileattr_get/set

LU-15969 llite: add support for  ->fileattr_get/set

From Linux 5.13, FS_IOC_SETFLAGS and GETFLAGS aren't passed down to
the filesystem, we need ->fileattr_get/set inode_operations instead.

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I7c13640012f3e3b6176bcdcc78a07f30e0667cbb
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50649
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>