tool_doswin: fix to use curl socket functions

Replace `WSASocketW()` with `CURL_SOCKET()`. Also replace a call
to `socketclose()` with `sclose()`. According to a comment,
`socketclose()` was chosen to silence test 1498 (and 2300) reporting
`MEMORY FAILURE`. These reports were accurate, and were caused by
calling `WSASocketW()` instead of `socket()` (now `CURL_SOCKET()`).

This also fixes the curl `sclose()` call on an error branch, which is
now correctly paired with a curl socket open. The mismatched open/close
calls caused an issue in TrackMemory-enabled (aka `CURLDEBUG`) builds.

Docs confirm that `socket()` is defaulting to overlapped I/O, matching
the replaced `WSASocketW()` call:
https://learn.microsoft.com/windows/win32/api/winsock2/nf-winsock2-socket#remarks

Also:
- checksrc: ban `WSASocket*()` functions.
- report `SOCKERRNO` instead of `GetLastError()` for socket calls,
  to match the rest of the codebase.

Follow-up to 9a2663322c #17572

Closes #18633

scripts/checksrc.pl

@@ -74,6 +74,9 @@ my %banfunc = (
     "LoadLibraryEx" => 1,
     "LoadLibraryExA" => 1,
     "LoadLibraryExW" => 1,
+    "WSASocket" => 1,
+    "WSASocketA" => 1,
+    "WSASocketW" => 1,
     "_waccess" => 1,
     "_access" => 1,
     "access" => 1,