rtems: Allow to set ISR level 0 in SMP config

Update #3000.

cpukit/rtems/src/taskmode.c

@@ -56,6 +56,7 @@ rtems_status_code rtems_task_mode(
 #if defined(RTEMS_SMP)
   if (
     ( mask & RTEMS_INTERRUPT_MASK ) != 0
+      && _Modes_Get_interrupt_level( mode_set ) != 0
       && rtems_configuration_is_smp_enabled()
   ) {
     return RTEMS_NOT_IMPLEMENTED;

testsuites/smptests/smpunsupported01/init.c

@@ -45,7 +45,7 @@ static void test(void)
   mode = RTEMS_INTERRUPT_LEVEL(0);
   if (mode == 0) {
     sc = rtems_task_mode(mode, RTEMS_INTERRUPT_MASK, &mode);
-    rtems_test_assert(sc == RTEMS_NOT_IMPLEMENTED);
+    rtems_test_assert(sc == RTEMS_SUCCESSFUL);
   }
 
   mode = RTEMS_INTERRUPT_LEVEL(1);