selftests: netfilter: switch zone stress to socat

centos9 has nmap-ncat which doesn't like the '-q' option, use socat.
While at it, mark test skipped if needed tools are missing.

Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

tools/testing/selftests/netfilter/nft_zones_many.sh

···
 	ip netns del $ns
 }
 
-ip netns add $ns
-if [ $? -ne 0 ];then
-	echo "SKIP: Could not create net namespace $gw"
-	exit $ksft_skip
-fi
+checktool (){
+	if ! $1 > /dev/null 2>&1; then
+		echo "SKIP: Could not $2"
+		exit $ksft_skip
+	fi
+}
+
+checktool "nft --version" "run test without nft tool"
+checktool "ip -Version" "run test without ip tool"
+checktool "socat -V" "run test without socat tool"
+checktool "ip netns add $ns" "create net namespace"
 
 trap cleanup EXIT
 
···
 		local start=$(date +%s%3N)
 		i=$((i + 10000))
 		j=$((j + 1))
-		dd if=/dev/zero of=/dev/stdout bs=8k count=10000 2>/dev/null | ip netns exec "$ns" nc -w 1 -q 1 -u -p 12345 127.0.0.1 12345 > /dev/null
+		# nft rule in output places each packet in a different zone.
+		dd if=/dev/zero of=/dev/stdout bs=8k count=10000 2>/dev/null | ip netns exec "$ns" socat STDIN UDP:127.0.0.1:12345,sourceport=12345
 		if [ $? -ne 0 ] ;then
 			ret=1
 			break