added entrypoint script

data/Dockerfiles/netfilter/netfilter.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+backend=iptables
+
+nft list table ip filter &>/dev/null
+nftables_found=$?
+
+iptables -L &>/dev/null
+iptables_found=$?
+
+if [ $nftables_found -lt $iptables_found ]; then
+  backend=nftables
+fi
+
+if [ $nftables_found -gt $iptables_found ]; then
+  backend=iptables
+fi
+
+if [ $nftables_found -eq 0 ] && [ $nftables_found -eq $iptables_found ]; then
+  nftables_lines=$(nft list ruleset | wc -l)
+  iptables_lines=$(iptables-save | wc -l)
+  if [ $nftables_lines -gt $iptables_lines ]; then
+    backend=nftables
+  else
+    backend=iptables
+  fi
+fi
+
+exec python -u server.py $backend