gstdtlscertificate: Define _WINSOCKAPI_ before including windows.h

gstdtlscertificate: Define _WINSOCKAPI_ before including windows.h

This avoid a build failure when compiling against OpenSSL 3.2.0. The
problem is when windows.h is included before WinSock2.h. Because
windows.h includes winsock.h[1]. Defining _WINSOCKAPI_ stops windows.h
including winsock.h.

Error:
```
[748/1041] Compiling C object ext/dtls/gstdtls.dll.p/gstdtlscertificate.c.obj
FAILED: ext/dtls/gstdtls.dll.p/gstdtlscertificate.c.obj
[...]
Windows Kits\10\include\10.0.17763.0\shared\ws2def.h(235): error C2011: 'sockaddr': 'struct' type redefinition
Windows Kits\10\include\10.0.17763.0\um\winsock.h(482): note: see declaration of 'sockaddr'
```

[1] https://stackoverflow.com/a/1372836

Closes: https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/3167
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5783>