src: fix windows build error from 221c689e

Just forward declare struct sockaddr, the struct is never actually
dereferenced in src/node_internals.h.

Before this commit, it included sys/socket.h but that header doesn't
exist on Windows.

src/node_internals.h

@@ -25,11 +25,10 @@
 #include <assert.h>
 #include <stdlib.h>
 
-#include <sys/types.h>
-#include <sys/socket.h>
-
 #include "v8.h"
 
+struct sockaddr;
+
 namespace node {
 
 // Defined in node.cc