selftests/bpf: Use connect_fd_to_fd in bpf_tcp_ca

To simplify the code, use BPF selftests helper connect_fd_to_fd() in
bpf_tcp_ca.c instead of open-coding it. This helper is defined in
network_helpers.c, and exported in network_helpers.h, which is already
included in bpf_tcp_ca.c.
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/e105d1f225c643bee838409378dd90fd9aabb6dc.1711447102.git.tanggeliang@kylinos.cnSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>

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

@@ -79,11 +79,9 @@ static void *server(void *arg)
 
 static void do_test(const char *tcp_ca, const struct bpf_map *sk_stg_map)
 {
-	struct sockaddr_in6 sa6 = {};
 	ssize_t nr_recv = 0, bytes = 0;
 	int lfd = -1, fd = -1;
 	pthread_t srv_thread;
-	socklen_t addrlen = sizeof(sa6);
 	void *thread_ret;
 	char batch[1500];
 	int err;
@@ -104,10 +102,6 @@ static void do_test(const char *tcp_ca, const struct bpf_map *sk_stg_map)
 	    settimeo(lfd, 0) || settimeo(fd, 0))
 		goto done;
 
-	err = getsockname(lfd, (struct sockaddr *)&sa6, &addrlen);
-	if (!ASSERT_NEQ(err, -1, "getsockname"))
-		goto done;
-
 	if (sk_stg_map) {
 		err = bpf_map_update_elem(bpf_map__fd(sk_stg_map), &fd,
 					  &expected_stg, BPF_NOEXIST);
@@ -116,7 +110,7 @@ static void do_test(const char *tcp_ca, const struct bpf_map *sk_stg_map)
 	}
 
 	/* connect to server */
-	err = connect(fd, (struct sockaddr *)&sa6, addrlen);
+	err = connect_fd_to_fd(fd, lfd, 0);
 	if (!ASSERT_NEQ(err, -1, "connect"))
 		goto done;