tests/shell: Test flush and nat chain recreate in one go

This tests what kernel commit ae6153b50f9bf ("netfilter: nf_tables:
permit second nat hook if colliding hook is going away") fixed for.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>

tests/shell/testcases/transactions/0041nat_restore_0

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+set -e
+
+RULESET="
+add table ip t
+add chain ip t c { type nat hook postrouting priority 0; }
+"
+
+$NFT -f - <<< $RULESET
+
+RULESET="
+flush ruleset
+$RULESET
+"
+
+$NFT -f - <<< $RULESET