More cleanups to separate main code from platform support and UI support, plus a few bugfixes.

src/network/slirp/tcp_subr.c

@@ -40,6 +40,9 @@
 
 #define WANT_SYS_IOCTL_H
 #include <stdlib.h>
+#ifndef WIN32
+# include <unistd.h>
+#endif
 #include "slirp.h"
 
 /* patchable/settable parameters for tcp */