rtems_task_restart() may be called from within interrupt context. So
checking only that the thread to restart is equal to the executing
thread is insufficient to determine a self restart. We have to also
check that no ISR is in progress. Merge _Thread_Restart_other() and
_Thread_Restart_self() into one _Thread_Restart() since they share a lot
of common code.
Close#4412.
73ebf9a27e