selftests/bpf: Monitor traffic for sockmap_listen.

Enable traffic monitor for each subtest of sockmap_listen.
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Link: https://lore.kernel.org/r/20240815053254.470944-6-thinker.li@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/prog_tests/sockmap_listen.c

@@ -1925,6 +1925,7 @@ static void test_udp_unix_redir(struct test_sockmap_listen *skel, struct bpf_map
 				int family)
 {
 	const char *family_name, *map_name;
+	struct netns_obj *netns;
 	char s[MAX_TEST_NAME];
 
 	family_name = family_str(family);
@@ -1932,8 +1933,15 @@ static void test_udp_unix_redir(struct test_sockmap_listen *skel, struct bpf_map
 	snprintf(s, sizeof(s), "%s %s %s", map_name, family_name, __func__);
 	if (!test__start_subtest(s))
 		return;
+
+	netns = netns_new("sockmap_listen", true);
+	if (!ASSERT_OK_PTR(netns, "netns_new"))
+		return;
+
 	inet_unix_skb_redir_to_connected(skel, map, family);
 	unix_inet_skb_redir_to_connected(skel, map, family);
+
+	netns_free(netns);
 }
 
 static void run_tests(struct test_sockmap_listen *skel, struct bpf_map *map,