update submodule to v3.1.5

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

diff --git a/upstream b/upstream
index 650a3f15cfa8166a8d0763042b4acd39b12afde2..23db6cba49b6bca811e5d08091e000e260649ee5 160000 (submodule)
--- a/upstream
+++ b/upstream
@@ -1 +1 @@
-Subproject commit 650a3f15cfa8166a8d0763042b4acd39b12afde2
+Subproject commit 23db6cba49b6bca811e5d08091e000e260649ee5