selftests: netfilter: place checktool helper in lib.sh

... so it doesn't have to be repeated everywhere.
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240411233624.8129-10-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -11,11 +11,7 @@
 
 source lib.sh
 
-nft --version > /dev/null 2>&1
-if [ $? -ne 0 ];then
-	echo "SKIP: Could not run test without nft tool"
-	exit $ksft_skip
-fi
+checktool "nft --version" "run test without nft tool"
 
 cleanup() {
 	cleanup_all_ns

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

@@ -24,13 +24,6 @@ source lib.sh
 
 rx=$(mktemp)
 
-checktool (){
-	if ! $1 > /dev/null 2>&1; then
-		echo "SKIP: Could not $2"
-		exit $ksft_skip
-	fi
-}
-
 checktool "iptables --version" "run test without iptables"
 checktool "socat -h" "run test without socat"
 

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

 net_netfilter_dir=$(dirname "$(readlink -e "${BASH_SOURCE[0]}")")
 
 source "$net_netfilter_dir/../lib.sh"
+
+checktool (){
+	if ! $1 > /dev/null 2>&1; then
+		echo "SKIP: Could not $2"
+		exit $ksft_skip
+	fi
+}