test-network: stop networkd and its socket

test-network: stop networkd and its socket

With the changes from 2c0dffe82db574b6b9e850e48f444674e4e1d7ea, starting
systemd-networkd.service will also activate systemd-networkd.socket.
When tearing down a test, we need to stop the socket as well, to make
sure networkd can't be activated accidentally with the wrong
configuration.

(cherry picked from commit 3aa645f0c0bb7697ef397ffef4647ff105d98fda)

Gbp-Pq: Name test-network-stop-networkd-and-its-socket.patch