stub: fix a io_queue_size limitation

io_queue_size is 256(default) in stub.c, it probably be a limitation
for some performance testing.

Change-Id: Iaf4a15966e7b814323bd8bf134d8f657635aca8e
Signed-off-by: Hailiang Wang <hailiangx.e.wang@intel.com>
Reviewed-on: https://review.gerrithub.io/394168
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>

test/app/stub/stub.c

@@ -55,6 +55,11 @@ static bool
 probe_cb(void *cb_ctx, const struct spdk_nvme_transport_id *trid,
 	 struct spdk_nvme_ctrlr_opts *opts)
 {
+	/*
+	 * Set the io_queue_size to UINT16_MAX to initialize
+	 * the controller with the possible largest queue size.
+	 */
+	opts->io_queue_size = UINT16_MAX;
 	return true;
 }