Notable upstream pull request merges:
#15839c3f2f1aa2 vdev probe to slow disk can stall mmp write checker
#158885044c4e3f Fast Dedup: ZAP Shrinking
#15996db499e68f Overflowing refreservation is bad
#1611867d13998b Make more taskq parameters writable
#1612821bc066ec Fix updating the zvol_htable when renaming a zvol
#16130645b83307 Improve write issue taskqs utilization
#161318fd3a5d02 Slightly improve dnode hash
#16134a6edc0adb zio: try to execute TYPE_NULL ZIOs on the current task
#16141b28461b7c Fix arcstats for FreeBSD after zfetch support
Obtained from: OpenZFS
OpenZFS commit: 8f1b7a6fa6