The code never set "iface_get_config->cidr_addr", despite
setting "cidr_prefix" and "has_cidr". As a result, cloud-setup
would think that the subnet is "0.0.0.0/$PLEN", and calculate
the gateway as "0.0.0.1".
As a result it would add a default route to table 30400 via 0.0.0.1,
which is obviously wrong.
How to detect the right gateway? Let's try obtain the subnet also via
the meta data. That seems mostly correct, except that we only access
subnet at index 0. What if there are multiple ones? I don't know.
https://bugzilla.redhat.com/show_bug.cgi?id=1912236
It's questionable whether the manual page should explain
exactly what it does.
However, it's a good exercise writing this up (to review
what happens). Also, a manual page that simply says "it configures
the network automatically" without going into how exactly, is
not very useful either.
