update ZFS submodule to 2.2.3-pve2

no real semantic change for the kernel module since the last update

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

diff --git a/submodules/zfsonlinux b/submodules/zfsonlinux
index 68be554e71e0cac3144d19930898f95bf6616620..3968b96ed4bb3aac1c82d410e4067c63f45ce84e 160000 (submodule)
--- a/submodules/zfsonlinux
+++ b/submodules/zfsonlinux
@@ -1 +1 @@
-Subproject commit 68be554e71e0cac3144d19930898f95bf6616620
+Subproject commit 3968b96ed4bb3aac1c82d410e4067c63f45ce84e