tidy-up: prefer return over exit(), fix fallouts

To avoid breaking the control flow and align to majority of code
already using `return`.

`exit()` has the side-effect of suppressing leak detection in cases.
Fix fallouts detected after switching to `return`.

- configure:
  - fix `getaddrinfo` run test to call `freeaddrinfo()` to pacify ASAN,
    and call `WSACleanup()` to deinit winsock2.
  - fix `getifaddrs` run test to call `freeifaddrs()` to pacify ASAN.
- tests/server:
  - setup `atexit(win32_cleanup)` via `win32_init()`.
  - return 2 instead of 1 on winsock2 init failures.
  - sws: goto cleanup instead of `exit()` in `http_connect()`.
    Follow-up to 02dfe71937 #7235
- tests/client/http:
  - cleanup memory to pacify ASAN in `h2-upgrade-extreme`,
    `tls-session-reuse`.
- examples:
  - block_ip: fix memory leak reported by CI.
  - http2-upload: avoid handle leaks.

Untouched `exit()` calls, made from callbacks:
- docs/examples: ephiperfifo.c, ghiper.c, hiperfifo.c
- tests/libtest: lib582.c, lib655.c, lib670.c
- tests/server: tftpd.c

Closes #16507

docs/examples/cookie_interface.c

@@ -34,8 +34,7 @@
 #include <curl/curl.h>
 #include <curl/mprintf.h>
 
-static void
-print_cookies(CURL *curl)
+static int print_cookies(CURL *curl)
 {
   CURLcode res;
   struct curl_slist *cookies;
@@ -47,7 +46,7 @@ print_cookies(CURL *curl)
   if(res != CURLE_OK) {
     fprintf(stderr, "Curl curl_easy_getinfo failed: %s\n",
             curl_easy_strerror(res));
-    exit(1);
+    return 1;
   }
   nc = cookies;
   i = 1;
@@ -60,6 +59,8 @@ print_cookies(CURL *curl)
     printf("(none)\n");
   }
   curl_slist_free_all(cookies);
+
+  return 0;
 }
 
 int