Cygwin: cleanup header including within network-releated files

* Rearrange includes and drop unneccessary ones.

* Don't pull in cygwin/socket.h into sys/un.h just to get
  sa_family_t.  Include sys/types.h and use __sa_family_t instead.

* start including Windows headers using the w32api/ path prefix

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/include/sys/un.h

@@ -9,14 +9,15 @@ details. */
 #ifndef _SYS_UN_H
 #define _SYS_UN_H
 
+#include <sys/types.h>
 #include <string.h>		/* for strlen */
-#include <cygwin/socket.h>
+
 
 /* POSIX requires only at least 100 bytes */
 #define UNIX_PATH_MAX   108
 
 struct sockaddr_un {
-  sa_family_t	 sun_family;              /* address family AF_LOCAL/AF_UNIX */
+  __sa_family_t	 sun_family;              /* address family AF_LOCAL/AF_UNIX */
   char	         sun_path[UNIX_PATH_MAX]; /* 108 bytes of socket address     */
 };