Revert "SUP-862 dsl_prop_register and dsl_sync_task_group_wait deadlock for read lock on dp->dp_config_rwlock they already own"

This reverts commit 65497981a1c94ed26504604cc17d073e9308e528.
This reverts commit e5460cde642509b12f6d8da622ac417afa8bc979.
This reverts commit a168d192769fce82a1fa1a34a5722f73afe3f3fd.
This reverts commit eb39b0745248cd0681141ee3acc04f59c724ab7a.
Merge pull request #130 in OS/nza-kernel from ~SASO.KISELKOV/nza-kernel:stable-3.1-SUP862-backout to stable-3.1

* commit '11e2c0ab01e43a70ecec221ef5952c12c8611522':
  Revert "SUP-862 dsl_prop_register and dsl_sync_task_group_wait deadlock for read lock on dp->dp_config_rwlock they already own"