update ZFS to 2.2.2

There shouldn't be any changes for us w.r.t. data integrity and the
recent uncovered dnode dirtiness, as we backported those patches
already.

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

diff --git a/submodules/zfsonlinux b/submodules/zfsonlinux
index 00036e5a6eba553a9f6d116c52c7189f773ac24d..81d11761c3a2d325b1b434247894365119ce22eb 160000 (submodule)
--- a/submodules/zfsonlinux
+++ b/submodules/zfsonlinux
@@ -1 +1 @@
-Subproject commit 00036e5a6eba553a9f6d116c52c7189f773ac24d
+Subproject commit 81d11761c3a2d325b1b434247894365119ce22eb