remote vdev via tcp, rdma etc.

[tiehexue]

I created a pull request in openzfsonwindows, which add a new vdev type named vdev_remote. With remote vdev, we can create zpool with remote raw image file or raw disk. Is this useful in any scenario?

1. create a remote vdev, tcp endpoint
   zfs_remoted -f a.img -p 9000
   or
   zfs_remoted -d physicaldrive2 -p 900

2. create a zpool
   zpool create tank remote://127.0.0.1:9000

It works in windows, and should not be difficult to works in Linux/FreeBSD/MacOS. And many much more optimization can be applied.

openzfsonwindows#578

[tonyhutter]

Windows 11 Pro supports iSCSI