selftests/bpf: Use post_socket_cb in start_server_str

This patch uses start_server_str() helper in test_dctcp_fallback() in
bpf_tcp_ca.c, instead of using start_server() and settcpca(). For
support opts in start_server_str() helper, opts->cb_opts needs to be
passed to post_socket_cb() in __start_server().
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/414c749321fa150435f7fe8e12c80fec8b447c78.1716638248.git.tanggeliang@kylinos.cnSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/network_helpers.c

@@ -94,7 +94,8 @@ static int __start_server(int type, const struct sockaddr *addr, socklen_t addrl
 	if (settimeo(fd, opts->timeout_ms))
 		goto error_close;
 
-	if (opts->post_socket_cb && opts->post_socket_cb(fd, NULL)) {
+	if (opts->post_socket_cb &&
+	    opts->post_socket_cb(fd, opts->cb_opts)) {
 		log_err("Failed to call post_socket_cb");
 		goto error_close;
 	}

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

@@ -187,6 +187,9 @@ static void test_dctcp_fallback(void)
 	};
 	struct bpf_dctcp *dctcp_skel;
 	struct bpf_link *link = NULL;
+	struct cb_opts dctcp = {
+		.cc = "bpf_dctcp",
+	};
 	struct cb_opts cubic = {
 		.cc = "cubic",
 	};
@@ -204,9 +207,9 @@ static void test_dctcp_fallback(void)
 	if (!ASSERT_OK_PTR(link, "dctcp link"))
 		goto done;
 
-	lfd = start_server(AF_INET6, SOCK_STREAM, "::1", 0, 0);
-	if (!ASSERT_GE(lfd, 0, "lfd") ||
-	    !ASSERT_OK(settcpca(lfd, "bpf_dctcp"), "lfd=>bpf_dctcp"))
+	opts.cb_opts = &dctcp;
+	lfd = start_server_str(AF_INET6, SOCK_STREAM, "::1", 0, &opts);
+	if (!ASSERT_GE(lfd, 0, "lfd"))
 		goto done;
 
 	opts.cb_opts = &cubic;