update ZFS to 2.2.4 staging for better 6.8 compat

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

diff --git a/submodules/zfsonlinux b/submodules/zfsonlinux
index 6c9ff9b992b46b2ba7c7b8ab9b5eaf35fff17158..68be554e71e0cac3144d19930898f95bf6616620 160000 (submodule)
--- a/submodules/zfsonlinux
+++ b/submodules/zfsonlinux
@@ -1 +1 @@
-Subproject commit 6c9ff9b992b46b2ba7c7b8ab9b5eaf35fff17158
+Subproject commit 68be554e71e0cac3144d19930898f95bf6616620