MFV r294793:
6367 spa_config_tryenter incorrectly handles the multiple-lock case

Reviewed by: Alek Pinchuk <alek.pinchuk@nexenta.com>
Reviewed by: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>
Reviewed by: Prashanth Sreenivasa <prashksp@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan McDonald <danmcd@omniti.com>
Reviewed by: Steven Hartland <steven.hartland@multiplay.co.uk>
Approved by: Matthew Ahrens <mahrens@delphix.com>

illumos/illumos-gate@e495b6e6735b803e422025a630352ef9bba788c5