MFV r322227: 8377 Panic in bookmark deletion

MFV r322227: 8377 Panic in bookmark deletion

illumos/illumos-gate@42418f9e73f0d007aa87675ecc206c26fc8e073e
https://github.com/illumos/illumos-gate/commit/42418f9e73f0d007aa87675ecc206c26fc8e073e

https://www.illumos.org/issues/8377
  The problem is that when dsl_bookmark_destroy_check() is executed from open
  context (the pre-check), it fills in dbda_success based on the existence of the
  bookmark.
  But the bookmark (or containing filesystem as in this case) can be destroyed
  before we get to syncing context. When we re-run dsl_bookmark_destroy_check()
  in syncing
  context, it will not add the deleted bookmark to dbda_success, intending for
  dsl_bookmark_destroy_sync() to not process it. But because the bookmark is
  still in dbda_success
  from the open-context call, we do try to destroy it.
  The fix is that dsl_bookmark_destroy_check() should not modify dbda_success
  when called from open context.

Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Matthew Ahrens <mahrens@delphix.com>

MFC after:	2 weeks