update lxc to include fixes for cgroupv2 setups

This commit fast-forwards 7 commits from upstream/master. The first commit
(partially) fixes a missing apparmor rule for /proc/sys/kernel/random/boot_id)

The last commit fixes running containers in pure cgroupv2 environments (by
premounting cgroup2).

It contains one other fix for a netlink bug, which I haven't seen in our
support channels, thus assume limited potential for regressions.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

diff --git a/lxc b/lxc
index 538337ee9dc5ca385cc8d9b6faaac1575c014a1b..4547e73e3e1c7f7a9fc88da6ac3276d99df1c5ec 160000 (submodule)
--- a/lxc
+++ b/lxc
@@ -1 +1 @@
-Subproject commit 538337ee9dc5ca385cc8d9b6faaac1575c014a1b
+Subproject commit 4547e73e3e1c7f7a9fc88da6ac3276d99df1c5ec