selftests: netfilter: nft_zones_many.sh: set ct sysctl after ruleset load

nf_conntrack_udp_timeout sysctl only exist once conntrack module is loaded,
if this test runs standalone on a modular kernel sysctl setting fails,
this can result in test failure as udp conntrack entries expire too fast.
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/r/20240422102546.2494-1-fw@strlen.deSigned-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -28,7 +28,6 @@ fi
 test_zones() {
 	local max_zones=$1
 
-ip netns exec "$ns1" sysctl -q net.netfilter.nf_conntrack_udp_timeout=3600
 ip netns exec "$ns1" nft -f /dev/stdin<<EOF
 flush ruleset
 table inet raw {
@@ -46,6 +45,9 @@ if [ "$?" -ne 0 ];then
 	echo "SKIP: Cannot add nftables rules"
 	exit $ksft_skip
 fi
+
+	ip netns exec "$ns1" sysctl -q net.netfilter.nf_conntrack_udp_timeout=3600
+
 	(
 		echo "add element inet raw rndzone {"
 	for i in $(seq 1 "$max_zones");do