MFV 286544:
5630 stale bonus buffer in recycled dnode_t leads to data corruption

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george@delphix.com>
Reviewed by: Will Andrews <will@freebsd.org>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Justin T. Gibbs <justing@spectralogic.com>