Is there a way to delete all iptables rules, that relate to a given interface? I don't see any command line option for this, may be there is a shorcut bash script for this?
Some possibilities, depending on your setup.
If you are running a quite simple structure of chains and dont to nesting and implications, use iptables-save to save your firewallset. Remove all lines with -i $if or -o $if, depending on your needs. Use grep or something. Save that ruleset, diff it to your first saved ruleset and if it's okay, load it with iptables-restore.
Alternatively - gather your rules in interface-specific chains. That way you can easily migrate or remove interfaces. And you are going speed up your firewall processing!
Add a rule to accept all the trafic on one interface :
To delete all the firewall rules (I have a doubt in reading your text),