Fix a minor style consistency issue.

When getting a string buffer for a string we just created, use
PyString_AS_STRING() instead of PyString_AsString() to avoid the
call overhead and extra type check.

Modules/socketmodule.c

@@ -989,7 +989,7 @@ PySocketSock_getsockopt(PySocketSockObject *s, PyObject *args)
 	if (buf == NULL)
 		return NULL;
 	res = getsockopt(s->sock_fd, level, optname,
-			 (void *)PyString_AsString(buf), &buflen);
+			 (void *)PyString_AS_STRING(buf), &buflen);
 	if (res < 0) {
 		Py_DECREF(buf);
 		return PySocket_Err();