selftests/bpf/test_tcp_check_syncookie: use temp netns for testing

Use temp netns instead of hard code name for testing in case the
netns already exists.

Signed-off-by: Hangbin Liu <[e-mail]>
Acked-by: Lorenz Bauer <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/test_tcp_check_syncookie.sh

···
 # Copyright (c) 2019 Cloudflare
 
 set -eu
+readonly NS1="ns1-$(mktemp -u XXXXXX)"
 
 wait_for_ip()
 {
···
 
 ns1_exec()
 {
-	ip netns exec ns1 "$@"
+	ip netns exec ${NS1} "$@"
 }
 
 setup()
 {
-	ip netns add ns1
+	ip netns add ${NS1}
 	ns1_exec ip link set lo up
 
 	ns1_exec sysctl -w net.ipv4.tcp_syncookies=2