socket.onclose() (#1364)

* Add socket.onclose() and close socket immediately when socket channel closed by peer

* Revert read_socket(), Add SOCKET_MORE, See #1358

* remove warning log , because it's not a rare case any more. See #1358

skynet-src/socket_server.h

@@ -13,7 +13,10 @@
 #define SOCKET_EXIT 5
 #define SOCKET_UDP 6
 #define SOCKET_WARNING 7
-#define SOCKET_RST 8 // Only for internal use
+
+// Only for internal use
+#define SOCKET_RST 8
+#define SOCKET_MORE 9
 
 struct socket_server;