- When VFS_VGET() is not supported, switch to VOP_LOOKUP(). - We are fine by only share-locking the vnode. - Remove assertion that doesn't hold for ZFS where we cross mount points   boundaries by going into .zfs/snapshot/<name>/.
- When VFS_VGET() is not supported, switch to VOP_LOOKUP().
- We are fine by only share-locking the vnode.
- Remove assertion that doesn't hold for ZFS where we cross mount points
  boundaries by going into .zfs/snapshot/<name>/.

Reviewed by:	rmacklem
MFC after:	1 month

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