Test with the new (~ppa4) version LGTM:

...
Unpacking libvirt0:amd64 (4.6.0-1ubuntu1~ppa4) over (4.0.0-1ubuntu13) ...
Processing triggers for ureadahead (0.100.0-20) ...
Setting up libjansson4:amd64 (2.11-1) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for systemd (237-3ubuntu10) ...
Processing triggers for man-db (2.8.4-2) ...
Setting up libvirt0:amd64 (4.6.0-1ubuntu1~ppa4) ...
Setting up libvirt-daemon (4.6.0-1ubuntu1~ppa4) ...
Setting up libvirt-clients (4.6.0-1ubuntu1~ppa4) ...
Setting up libvirt-daemon-system (4.6.0-1ubuntu1~ppa4) ...
Installing new version of config file /etc/apparmor.d/abstractions/libvirt-qemu ...
Installing new version of config file /etc/apparmor.d/usr.sbin.libvirtd ...
Installing new version of config file /etc/default/libvirt-guests ...
Installing new version of config file /etc/libvirt/libvirtd.conf ...
Installing new version of config file /etc/libvirt/libxl.conf ...
Installing new version of config file /etc/libvirt/qemu.conf ...
Installing new version of config file /etc/libvirt/virtlockd.conf ...
Installing new version of config file /etc/libvirt/virtlogd.conf ...
Created symlink /etc/systemd/system/sockets.target.wants/virtlockd-admin.socket → /lib/systemd/system/virtlockd-admin.socket.
Created symlink /etc/systemd/system/sockets.target.wants/virtlogd-admin.socket → /lib/systemd/system/virtlogd-admin.socket.
virtlockd.service is a disabled or a static unit, not starting it.
virtlogd.service is a disabled or a static unit, not starting it.
Setting up libvirt-daemon dnsmasq configuration.
Setting up libvirt-daemon-driver-storage-rbd (4.6.0-1ubuntu1~ppa4) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...


After this even the admin socket started just fine.

Status after upgrade:
root@c2:~# systemctl status virtlogd.service virtlogd.socket virtlogd-admin.socket virtlockd.service virtlockd.socket virtlockd-admin.socket --no-pager --lines 2
● virtlogd.service - Virtual machine log manager
   Loaded: loaded (/lib/systemd/system/virtlogd.service; indirect; vendor preset: enabled)
   Active: active (running) since Thu 2018-08-09 11:57:04 UTC; 43s ago
     Docs: man:virtlogd(8)
           https://libvirt.org
 Main PID: 5889 (virtlogd)
    Tasks: 1 (limit: 4915)
   CGroup: /system.slice/virtlogd.service
           └─5889 /usr/sbin/virtlogd

Aug 09 11:57:05 c2 systemd[1]: virtlogd.service: Failed to reset devices.list: Operation not permitted
Aug 09 11:57:05 c2 systemd[1]: virtlogd.service: Failed to reset devices.list: Operation not permitted

● virtlogd.socket - Virtual machine log manager socket
   Loaded: loaded (/lib/systemd/system/virtlogd.socket; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-08-09 11:57:04 UTC; 43s ago
   Listen: /var/run/libvirt/virtlogd-sock (Stream)
   CGroup: /system.slice/virtlogd.socket
Failed to dump process list, ignoring: No such file or directory

Aug 09 11:57:04 c2 systemd[1]: Stopping Virtual machine log manager socket.
Aug 09 11:57:04 c2 systemd[1]: Listening on Virtual machine log manager socket.

● virtlogd-admin.socket - Virtual machine log manager socket
   Loaded: loaded (/lib/systemd/system/virtlogd-admin.socket; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-08-09 11:57:04 UTC; 43s ago
   Listen: /var/run/libvirt/virtlogd-admin-sock (Stream)
   CGroup: /system.slice/virtlogd-admin.socket
Failed to dump process list, ignoring: No such file or directory

Aug 09 11:57:04 c2 systemd[1]: Listening on Virtual machine log manager socket.

● virtlockd.service - Virtual machine lock manager
   Loaded: loaded (/lib/systemd/system/virtlockd.service; indirect; vendor preset: enabled)
   Active: inactive (dead)
     Docs: man:virtlockd(8)
           https://libvirt.org

● virtlockd.socket - Virtual machine lock manager socket
   Loaded: loaded (/lib/systemd/system/virtlockd.socket; enabled; vendor preset: enabled)
   Active: active (listening) since Thu 2018-08-09 11:57:04 UTC; 43s ago
   Listen: /var/run/libvirt/virtlockd-sock (Stream)
   CGroup: /system.slice/virtlockd.socket
Failed to dump process list, ignoring: No such file or directory

Aug 09 11:57:04 c2 systemd[1]: Stopping Virtual machine lock manager socket.
Aug 09 11:57:04 c2 systemd[1]: Listening on Virtual machine lock manager socket.

● virtlockd-admin.socket - Virtual machine lock manager admin socket
   Loaded: loaded (/lib/systemd/system/virtlockd-admin.socket; enabled; vendor preset: enabled)
   Active: active (listening) since Thu 2018-08-09 11:57:05 UTC; 42s ago
   Listen: /var/run/libvirt/virtlockd-admin-sock (Stream)
   CGroup: /system.slice/virtlockd-admin.socket
Failed to dump process list, ignoring: No such file or directory

Aug 09 11:57:05 c2 systemd[1]: Listening on Virtual machine lock manager admin socket.



The only potentially bad things is that virtlogd is listed as "started ... 43s ago" which would imply a restart that should not happen.