use skynet malloc api directly

skynet-src/socket_server.c

@@ -1,4 +1,3 @@
-// include skynet.h first for malloc hook
 #include "skynet.h"
 
 #include "socket_server.h"
@@ -128,8 +127,8 @@ union sockaddr_all {
 	struct sockaddr_in6 v6;
 };
 
-#define MALLOC malloc
-#define FREE free
+#define MALLOC skynet_malloc
+#define FREE skynet_free
 
 static void
 socket_keepalive(int fd) {