UC22 network setup crashes

To reproduce it, just freshly install UC22, and in subiquity, unconfigure the network. Apply. Then reconfigure it.

It will crash when subiquity calls "netplan apply", which will crash when calling "networkctl reload". And it is not possible to reconfigure.

The issue is more obvious on real hardware like raspberry pi, because network might not have configured itself before subiquity starts.

subiquity stops systemd-networkd since
https://github.com/canonical/subiquity/commit/41014408143ece5df9ef000d65c23f9307098905

netplan tries to reload systemd-networkd since
https://github.com/canonical/netplan/commit/3ec52c41d1a9b3c011c94f9644a02e99451f4330

These 2 commits are not compatible.

Start with the reported flow in subiquity: unconfigure and reconfigure the network on a fresh UC22 installation, then trace the netplan apply call through networkctl reload. Review the linked subiquity and netplan commits to understand their service-state interaction. Done means network reconfiguration completes without a crash, including on Raspberry Pi hardware.

Written by the indexing model from the issue text.