Wait for network config before activating libvirt socket

[DavidFair]

Wait for the network configuration to complete before trying to activate the libvirt socket. This prevents systemd binding to the specified IP, then having the interface either come up or reconfigure.

Due to the race-y nature of the network config (at least with NetworkManager) and the socket activation this would mean <50% of the machines rebooting would be affected. After this point the socket is "up" from systemd's POV however anything (including telnet) trying to open the port will find it closed until an administrator restarts the socket unit

[DavidFair]

Some more logs for context - I suspect D-bus restarting NM is causing the interface to go down and up, which causes the open socket to reset without systemd noticing or rebinding:

Dec 20 08:57:10 hv.example.com NetworkManager[3565]: <info>  [1734685030.6777] manager: (p-br0-o): new Veth device (/org/freedesktop/NetworkManager/Devices/9)
Dec 20 08:57:10 hv.example.com NetworkManager[3565]: <info>  [1734685030.6782] device (p-br0-o): state change: unmanaged -> unavailable (reason 'managed', sys-iface-state: 'external')
Dec 20 08:57:10 hv.example.com NetworkManager[3565]: <info>  [1734685030.6797] bus-manager: acquired D-Bus service "org.freedesktop.NetworkManager"
Dec 20 08:57:10 hv.example.com NetworkManager[3565]: <info>  [1734685030.6798] caught SIGTERM, shutting down normally.
Dec 20 08:57:10 hv.example.com NetworkManager[3565]: <info>  [1734685030.6879] exiting (success)
Dec 20 08:57:10 hv.example.com systemd[1]: NetworkManager.service: Deactivated successfully.
Dec 20 08:57:10 hv.example.com systemd[1]: Stopped Network Manager.
Dec 20 08:57:10 hv.example.com systemd[1]: Starting Network Manager...
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.7462] NetworkManager (version 1.48.10-2.el9_5) is starting... (after a restart, boot:67fa3089-ef37-42ab-a798-c4fa>
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.7464] Read config: /etc/NetworkManager/NetworkManager.conf 
...
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.7753] manager: (br0): new Bridge device (/org/freedesktop/NetworkManager/Devices/6)
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.7760] manager: (br0.1602): new VLAN device (/org/freedesktop/NetworkManager/Devices/7)
...
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.8790] device (br0): state change: secondaries -> activated (reason 'none', sys-iface-state: 'managed')
Dec 20 08:57:10 hv.example.com NetworkManager[4343]: <info>  [1734685030.8792] device (br0): Activation: successful, device activated.