fix(firewall): log warning if ipv6 nat filter not supported instead of returning an error

- Allow to port forward redirect for IPv4 and not IPv6 if IPv6 NAT is not supported
- Fix #2503

internal/firewall/interfaces.go

@@ -9,5 +9,6 @@ type CmdRunner interface {
 type Logger interface {
 	Debug(s string)
 	Info(s string)
+	Warn(s string)
 	Error(s string)
 }