Update vendor/illumos/dist and vendor-sys/illumos/dist
to illumos-gate 13959:e03e14ddfb4c
Illumos ZFS issues:
3552 condensing one space map burns 3 seconds of CPU in spa_sync() thread
3564 spa_sync() spends 5-10% of its time in metaslab_sync() (when not
condensing)