selftests/bpf: Fix a fd leak in an error path in network_helpers.c

In __start_server, it leaks a fd when setsockopt(SO_REUSEPORT) fails.
This patch fixes it.

Fixes: eed92af ("bpf: selftest: Test batching and bpf_(get|set)sockopt in bpf tcp iter")
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20230316000726.1016773-2-martin.lau@linux.dev

tools/testing/selftests/bpf/network_helpers.c

@@ -95,7 +95,7 @@ static int __start_server(int type, int protocol, const struct sockaddr *addr,
 	if (reuseport &&
 	    setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &on, sizeof(on))) {
 		log_err("Failed to set SO_REUSEPORT");
-		return -1;
+		goto error_close;
 	}
 
 	if (bind(fd, addr, addrlen) < 0) {