Installimage don't configure `pointtopoint` correctly

[morsik]

According to official Hetzner documentation:

Our standard images already come with this configuration so that all traffic is routed via the gateway.

And then followed by example:

## /etc/network/interfaces example Hetzner root server
# Loopback-Adapter
auto lo
iface lo inet loopback
#
# LAN interface
auto eth0
iface eth0 inet static
  # Main IP address of the server
  address 192.168.0.250
  # Netmask 255.255.255.255 (/32) independent from the
  # real subnet size (e.g. /27)
  netmask 255.255.255.255
  # explicit host route to the gateway
  gateway 192.168.0.1
  pointopoint 192.168.0.1

It seems that installimage script behave incorrectly, because after installing official Hetzner Debian image I see:

root@server ~ # cat /etc/network/interfaces
### Hetzner Online GmbH installimage

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback
iface lo inet6 loopback

auto eno1
iface eno1 inet static
  address 1.2.3.104   # 1.2.3 is my censor :)
  netmask 255.255.255.192
  gateway 1.2.3.65
  # route 1.2.3.64/26 via 1.2.3.65
  up route add -net 1.2.3.64 netmask 255.255.255.192 gw 1.2.3.65 dev eno1

iface eno1 inet6 static
  address XXX::2
  netmask 64
  gateway fe80::1

root@server ~ # ip r
default via 1.2.3.65 dev eno1 onlink
1.2.3.64/26 via 1.2.3.65 dev eno1
1.2.3.64/26 dev eno1 proto kernel scope link src 1.2.3.104

Instead of config I see on Ubuntu 24.04 for comparison (also from installimage):

root@another-server ~ # ip r
default via 5.6.7.1 dev enp7s0 proto static onlink

This later causes issues with automation like Ansible, because Ansible reads current network setup, and sees that the netmask is /32 instead of whatever is needed. And then breaks network configuration because it's not aware of weird up route (we have quite weird setup and we're just replacing whole /etc/network/interfaces with our config)