rcuperf: Set more user-friendly defaults

Common-case use of rcuperf must set rcuperf.nreaders=0 and if not built
as a module, rcuperf.shutdown.  This commit therefore sets the default
for rcuperf.nreaders to zero and sets the default for rcuperf.shutdown
to zero if rcuperf is built as a module and to one otherwise.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/rcuperf.c

@@ -63,9 +63,10 @@ torture_param(bool, gp_async, false, "Use asynchronous GP wait primitives");
 torture_param(int, gp_async_max, 1000, "Max # outstanding waits per reader");
 torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
 torture_param(int, holdoff, 10, "Holdoff time before test start (s)");
-torture_param(int, nreaders, -1, "Number of RCU reader threads");
+torture_param(int, nreaders, 0, "Number of RCU reader threads");
 torture_param(int, nwriters, -1, "Number of RCU updater threads");
-torture_param(bool, shutdown, false, "Shutdown at end of performance tests.");
+torture_param(bool, shutdown, !IS_ENABLED(MODULE),
+	      "Shutdown at end of performance tests.");
 torture_param(bool, verbose, true, "Enable verbose debugging printk()s");
 
 static char *perf_type = "rcu";