selftests: netfilter: conntrack_vrf.sh: prefer socat, not iperf3

Use socat, like most of the other scripts already do.  This also makes
the script complete slightly faster (3s -> 1s).

iperf3 establishes two connections (1 control connection, and 1+x
depending on test), so adjust expected counter values as well.
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240423130604.7013-8-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/netfilter/conntrack_vrf.sh

@@ -43,15 +43,9 @@ cleanup()
 	cleanup_all_ns
 }
 
-if ! nft --version > /dev/null 2>&1;then
-	echo "SKIP: Could not run test without nft tool"
-	exit $ksft_skip
-fi
-
-if ! conntrack --version > /dev/null 2>&1;then
-	echo "SKIP: Could not run test without conntrack tool"
-	exit $ksft_skip
-fi
+checktool "nft --version" "run test without nft"
+checktool "conntrack --version" "run test without conntrack"
+checktool "socat -h" "run test without socat"
 
 trap cleanup EXIT
 
@@ -79,7 +73,15 @@ ip -net "$ns1" li set veth0 up
 ip -net "$ns0" addr add $IP0/$PFXL dev veth0
 ip -net "$ns1" addr add $IP1/$PFXL dev veth0
 
-ip netns exec "$ns1" iperf3 -s > /dev/null 2>&1 &
+listener_ready()
+{
+        local ns="$1"
+
+        ss -N "$ns" -l -n -t -o "sport = :55555" | grep -q "55555"
+}
+
+ip netns exec "$ns1" socat -u -4 TCP-LISTEN:55555,reuseaddr,fork STDOUT > /dev/null &
+busywait $BUSYWAIT_TIMEOUT listener_ready "$ns1"
 
 # test vrf ingress handling.
 # The incoming connection should be placed in conntrack zone 1,
@@ -160,16 +162,16 @@ table ip nat {
 	}
 }
 EOF
-	if ! ip netns exec "$ns0" ip vrf exec tvrf iperf3 -t 1 -c $IP1 >/dev/null; then
-		echo "FAIL: iperf3 connect failure with masquerade + sport rewrite on vrf device"
+	if ! ip netns exec "$ns0" ip vrf exec tvrf socat -u -4 STDIN TCP:"$IP1":55555 < /dev/null > /dev/null;then
+		echo "FAIL: connect failure with masquerade + sport rewrite on vrf device"
 		ret=1
 		return
 	fi
 
 	# must also check that nat table was evaluated on second (lower device) iteration.
-	ip netns exec "$ns0" nft list table ip nat |grep -q 'counter packets 2' &&
-	if ip netns exec "$ns0" nft list table ip nat |grep -q 'untracked counter packets [1-9]'; then
-		echo "PASS: iperf3 connect with masquerade + sport rewrite on vrf device ($qdisc qdisc)"
+	if ip netns exec "$ns0" nft list table ip nat |grep -q 'counter packets 1' &&
+	   ip netns exec "$ns0" nft list table ip nat |grep -q 'untracked counter packets [1-9]'; then
+		echo "PASS: connect with masquerade + sport rewrite on vrf device ($qdisc qdisc)"
 	else
 		echo "FAIL: vrf rules have unexpected counter value"
 		ret=1
@@ -195,15 +197,15 @@ table ip nat {
 	}
 }
 EOF
-	if ! ip netns exec "$ns0" ip vrf exec tvrf iperf3 -t 1 -c $IP1 > /dev/null; then
-		echo "FAIL: iperf3 connect failure with masquerade + sport rewrite on veth device"
+	if ! ip netns exec "$ns0" ip vrf exec tvrf socat -u -4 STDIN TCP:"$IP1":55555 < /dev/null > /dev/null;then
+		echo "FAIL: connect failure with masquerade + sport rewrite on veth device"
 		ret=1
 		return
 	fi
 
 	# must also check that nat table was evaluated on second (lower device) iteration.
-	if ip netns exec "$ns0" nft list table ip nat |grep -q 'counter packets 2'; then
-		echo "PASS: iperf3 connect with masquerade + sport rewrite on veth device"
+	if ip netns exec "$ns0" nft list table ip nat |grep -q 'counter packets 1'; then
+		echo "PASS: connect with masquerade + sport rewrite on veth device"
 	else
 		echo "FAIL: vrf masq rule has unexpected counter value"
 		ret=1