test-network fails with a bad local host configuration

[keszybz]

I got bit by #717 again, and made an error in the configuration file. I guess that's on me.
But this also causes our unit tests to fail:

$ cat /etc/systemd/network/ens3.network 
[Network]
Name=ens3
DHCP=yes
$ build/test-network
/etc/systemd/network/ens3.network:2: Unknown lvalue 'Name' in section 'Network'
Assertion 'network_get(manager, loopback, "lo", &mac, &network) == -ENOENT' failed at ../src/network/test-network.c:126, function test_network_get(). Aborting.
Aborted (core dumped)