tests/server: sync wait_ms() with the libcurl implementation

It contains a series of bugfixes and updates applied to libcurl's
`Curl_wait_ms()` over the years, but missed from the copy in
`tests/server/util.c`:
- d65321f939,
  52e822173a,
  5912da253b
- 4a8f459837
- 1ad49feb71

It fixes `wait_ms()` to check for, and return `SOCKERRNO`. Fixing error
handling on Windows.

Also:
- tests/server: change callers to check `SOCKERRNO`.
- `wait_ms()`: fix to check for the correct error code on Windows.
  Pending for `Curl_wait_ms()`: #16621.
- `Curl_wait_ms()`: tidy-up `Sleep()` argument cast (nit).
- lib/curl_trc: drop an unused header.

Closes #16627

tests/server/sockfilt.c

@@ -1253,9 +1253,9 @@ static curl_socket_t sockfilt_sockdaemon(curl_socket_t sock,
         rc = wait_ms(delay);
         if(rc) {
           /* should not happen */
-          error = errno;
+          error = SOCKERRNO;
           logmsg("wait_ms() failed with error (%d) %s",
-                 error, strerror(error));
+                 error, sstrerror(error));
           sclose(sock);
           return CURL_SOCKET_BAD;
         }