Illumos 6367 - spa_config_tryenter incorrectly handles the multiple-lock case

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>

References:

https://www.illumos.org/issues/6367
https://github.com/illumos/illumos-gate/commit/e495b6e

Ported-by: kernelOfTruth kerneloftruth@gmail.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>