Os: Ubuntu 17.04
Assuming you have the firewall rules in:
/etc/iptables.up.rules
Perhaps the most obvious answer will be to create a file called iptables in:
/etc/network/if-pre-up.d
with the content:
#!/bin/bash
/sbin/iptables-restore < /etc/iptables.up.rules
and make it executable using
sudo chmod +x /etc/network/if-pre-up.d/iptables
This way before your network interface is activated your rules will be loaded.