selftests: mptcp: stop forcing iptables-legacy

Commit 0c4cd3f8 ("selftests: mptcp: join: use 'iptables-legacy' if
available") and commit a5a5990c ("selftests: mptcp: sockopt: use
'iptables-legacy' if available") forced using iptables-legacy if
available.

This was needed because of some issues that were visible when testing
the kselftests on a v5.15.x with iptables-nft as default backend. It
looks like these errors are no longer present. As mentioned by Pablo [1],
the errors were maybe due to missing kernel config. We can then use
iptables-nft if it is the default one, instead of using a legacy tool.

We can then check the variables iptables and ip6tables are valid. We can
keep the variables to easily change it later or add options.

Link: https://lore.kernel.org/netdev/ZbFiixyMFpQnxzCH@calendula/ [1]
Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/20240306-upstream-net-next-20240304-selftests-mptcp-shared-code-shellcheck-v2-1-bc79e6e5e6a0@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -167,15 +167,11 @@ check_tools()
 		exit $ksft_skip
 	fi
 
-	# Use the legacy version if available to support old kernel versions
-	if iptables-legacy -V &> /dev/null; then
-		iptables="iptables-legacy"
-		ip6tables="ip6tables-legacy"
-	elif ! iptables -V &> /dev/null; then
-		echo "SKIP: Could not run all tests without iptables tool"
+	if ! "${iptables}" -V &> /dev/null; then
+		echo "SKIP: Could not run all tests without ${iptables} tool"
 		exit $ksft_skip
-	elif ! ip6tables -V &> /dev/null; then
-		echo "SKIP: Could not run all tests without ip6tables tool"
+	elif ! "${ip6tables}" -V &> /dev/null; then
+		echo "SKIP: Could not run all tests without ${ip6tables} tool"
 		exit $ksft_skip
 	fi
 }

tools/testing/selftests/net/mptcp/mptcp_sockopt.sh

@@ -96,15 +96,11 @@ if [ $? -ne 0 ];then
 	exit $ksft_skip
 fi
 
-# Use the legacy version if available to support old kernel versions
-if iptables-legacy -V &> /dev/null; then
-	iptables="iptables-legacy"
-	ip6tables="ip6tables-legacy"
-elif ! iptables -V &> /dev/null; then
-	echo "SKIP: Could not run all tests without iptables tool"
+if ! "${iptables}" -V &> /dev/null; then
+	echo "SKIP: Could not run all tests without ${iptables} tool"
 	exit $ksft_skip
-elif ! ip6tables -V &> /dev/null; then
-	echo "SKIP: Could not run all tests without ip6tables tool"
+elif ! "${ip6tables}" -V &> /dev/null; then
+	echo "SKIP: Could not run all tests without ${ip6tables} tool"
 	exit $ksft_skip
 fi