Revert "Eliminate the zfsdev_state_lock entirely and replace it with the"

This reverts commit 1d8972b3f353f986eb5b85bc108b1c0d946d3218.

Conflicts:
	sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zvol.c
FreeBSD/ZFS snapshot handling fix
zfsctl_snapshot_lookup disabled for a possible deadlock