Add align to struct mg_iobuf

src/net.c

@@ -143,6 +143,7 @@ struct mg_connection *mg_alloc_conn(struct mg_mgr *mgr) {
       (struct mg_connection *) calloc(1, sizeof(*c) + mgr->extraconnsize);
   if (c != NULL) {
     c->mgr = mgr;
+    c->send.align = c->recv.align = MG_IO_SIZE;
     c->id = ++mgr->nextid;
   }
   return c;