Fix some nits in fork_exit() so it more properly duplicates the backend of mi_switch: - Set the oncpu value for the current thread. - Always set switchticks, not just in the SMP case. - Add a KTR entry for fork_exit that is the same as the "new proc"   entry in mi_switch(). - Release sched_lock a bit later like we do with mi_switch().
Fix some nits in fork_exit() so it more properly duplicates the backend
of mi_switch:
- Set the oncpu value for the current thread.
- Always set switchticks, not just in the SMP case.
- Add a KTR entry for fork_exit that is the same as the "new proc"
  entry in mi_switch().
- Release sched_lock a bit later like we do with mi_switch().

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase