Workaround inability to launch working enumerated Wi-Fi hotspot on Ubuntu 24.04

It seems that the nftables rules set by NetworkManager are buggy, we need to switch to iptables to fix internet connectivity from clients.

Create a /etc/NetworkManager/conf.d/90-workaround-hotspot-connectivity-problem.conf file with the following content:

# Workaround internet connectivity issues when the emulated Wi-Fi hotspot is enabled.
#
# References:
#
# * firewall-backend | `main` section | NetworkManager.conf: NetworkManager Reference Manual
#   https://networkmanager.pages.freedesktop.org/NetworkManager/NetworkManager/NetworkManager.conf.html#id-1.2.3.7
[main]
firewall-backend=iptables