Use io_uring SQ size for ringloop capacity - otherwise get_sqe could return NULL when space_left() was > 0 under load

Raise default io_uring size to 1024 for the same effective capacity as previously

src/osd_main.cpp

@@ -58,7 +58,7 @@ int main(int narg, char *args[])
     }
     signal(SIGINT, handle_sigint);
     signal(SIGTERM, handle_sigint);
-    ring_loop_t *ringloop = new ring_loop_t(512);
+    ring_loop_t *ringloop = new ring_loop_t(RINGLOOP_DEFAULT_SIZE);
     osd = new osd_t(config, ringloop);
     while (1)
     {