Update the Win32 miniperl conditional compilation, for the htonl etc changes.

As of commit 19253ae62cd13079 (Oct 2012), miniperl on Win32 avoids using
Winsock. The win32_* wrappers for htonl etc had used the pre-processor
macro MYSWAP to conditionally compile in the correct code. However, MYSWAP
was defined as a side effect of using the htonl etc wrappers in util.c,
which are no longer needed. Hence use the WIN32_NO_SOCKETS macro directly
in win32sck.c for the correct conditional compilation.