CVE-2026-43158 xfs: fix freemap adjustments when adding xattrs to leaf blocks

In the Linux kernel, the following vulnerability has been resolved: xfs: fix freemap adjustments when adding xattrs to leaf blocks xfs/592 and xfs/794 both trip this assertion in the leaf block freemap adjustment code after 20 minutes of running on my test VMs: ASSERTichdr-firstused = ichdr-count...