update to lxcfs-4.0.0 tag

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

diff --git a/lxcfs b/lxcfs
index 416809170b93bc75cf325e1db1eb7f47664c7845..6df0f969ee8a73ebae8f58acb91404cfb8c9cc14 160000 (submodule)
--- a/lxcfs
+++ b/lxcfs
@@ -1 +1 @@
-Subproject commit 416809170b93bc75cf325e1db1eb7f47664c7845
+Subproject commit 6df0f969ee8a73ebae8f58acb91404cfb8c9cc14