SMP: There were certain conditions that we must avoid by preventing releasing...

SMP: There were certain conditions that we must avoid by preventing releasing the pending tasks while withn a critical section.  But this logic was incomplete; there was no logic to prevent other CPUs from adding new, running tasks while on CPU is in a critical section.

This commit corrects this.  This is matching logic in sched_addreadytorun to avoid starting new tasks within the critical section (unless the CPU is the holder of the lock).  The holder of the IRQ lock must be permitted to do whatever it needs to do.