update ZFS to 2.1.6

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

diff --git a/submodules/zfsonlinux b/submodules/zfsonlinux
index 3f3541cad07018038b112fe1219895c210a30473..186fde725e63731d0c32913b5fe13dd562f15940 160000 (submodule)
--- a/submodules/zfsonlinux
+++ b/submodules/zfsonlinux
@@ -1 +1 @@
-Subproject commit 3f3541cad07018038b112fe1219895c210a30473
+Subproject commit 186fde725e63731d0c32913b5fe13dd562f15940