MFC r258311

  opensolaris/uts/common/dtrace/fasttrap.c
          Fix several problems that can cause panics on kldload and kldunload.

          * kproc_create(fasttrap_pid_cleanup_cb, ...) gets called before
            fasttrap_provs.fth_table gets allocated.  This can lead to a panic
            on module load, because fasttrap_pid_cleanup_cb references
            fasttrap_provs.fth_table.  Move kproc_create down after the point
            that fasttrap_provs.fth_table gets allocated, and modify the error
            handling accordingly.

          * dtrace_fasttrap_{fork,exec,exit} weren't getting NULLed until
            after fasttrap_provs.fth_table got freed.  That caused panics on
            module unload because fasttrap_exec_exit calls
            fasttrap_provider_retire, which references
            fasttrap_provs.fth_table.  NULL those function pointers earlier.

          * There wasn't any code to destroy the
            fasttrap_{tpoints,provs,procs}.fth_table mutexes on module unload,
            leading to a resource leak when WITNESS is enabled.  Destroy those
            mutexes during fasttrap_unload().

Sponsored by: Spectra Logic Corporation