ULE: provide defaults to ts_cpu

[wma]

Summary

Fix a bug when the system has no CPU 0. When created, threads were implicitly assigned to CPU 0. This had no practical effect since a real CPU was chosen immediately by the scheduler. However, on systems without a CPU 0, sched_ule attempted to access the scheduler queue of the "old" CPU when assigned the initial choice of the old one. This caused an attempt to use illegal memory and a crash (or, more usually, a deadlock). Fix this by assigned new threads to the BSP explicitly and add some asserts to see that this problem does not recur.

[• hselasky]

This patch is wrong. See discussions around r326218 on FreeBSD SVN mailing list.