5422 preserve AVL invariants in dn_dbufs
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Paul Dagnelie <paul.dagnelie@delphix.com>
Reviewed by: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>
Reviewed by: Albert Lee <trisk@nexenta.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Alex Reece <alex@delphix.com>

illumos/illumos-gate@a846f19d279fdfb0e0d63f78ccaf0205a88274d2